{"id":62,"slug":"62-dsip-head-to-tail-backbone-cyclization-via-amide-bond-between-trp","title":"DSIP head-to-tail cyclization to lock β-turn and resist exopeptidase degradation","status":"DISCARDED","fold_verdict":"DISCARDED","discard_reason":"target_not_predictable: no UniProt ID resolved — target identity unconfirmed","peptide":{"name":"DSIP","class":"PERFORMANCE","sequence":"WAGGDASGE","modified_sequence":"cyclo(WAGGDASGE)","modification_description":"Head-to-tail (backbone) cyclization via amide bond between Trp-1 α-amine and Glu-9 α-carboxylate, yielding cyclo(WAGGDASGE)"},"target":{"protein":"GABA-A receptor (benzodiazepine/neurosteroid-modulated chloride channel complex implicated in DSIP's","uniprot_id":null,"chembl_id":null,"gene_symbol":null},"rationale":{"hypothesis":"We hypothesize that head-to-tail backbone cyclization of DSIP — joining the Trp-1 α-amine to the Glu-9 α-carboxylate via a direct amide bond — will collapse the floppy nonapeptide into a constrained macrocycle that pre-organizes a β-turn-like bioactive shape. This single change simultaneously addresses DSIP's two principal liabilities: extreme conformational entropy (which dilutes any productive binding pose) and rapid exopeptidase clearance (which a previous N-acetyl/C-amide cap only partially mitigated, Fold #46). Boltz-2 / Chai-1 should resolve a single dominant macrocyclic conformer if the closure is geometrically feasible.","rationale":"DSIP is a 9-mer with two central glycines and no anchoring secondary structure — the linear peptide samples a vast conformational ensemble, which is why Fold #57's D-Ala rigidification was discarded (point mutations at the hinge are too local to fold the whole peptide). Head-to-tail cyclization is a more global constraint: it forces backbone closure and dramatically reduces accessible φ/ψ space, a strategy validated for short linear bioactives like somatostatin analogs and melanotan derivatives. It also blocks BOTH amino- and carboxypeptidase attack at the same time without introducing non-canonical chemistry. This diverges from the last 3 folds (Hyp substitution, C-terminal truncation, D-Ala double-sub) on both axes — Cyclization category has not appeared in the last 3 lab-wide folds, and CONFORMATION focus is fresh. Note: canonical target list is empty for DSIP, so UniProt/ChEMBL/gene IDs are null — Clinical agent will need to handle the no-bioactivity-data case.","predicted_outcome":"Structure prediction should yield a compact macrocyclic ring (~9-residue cycle, ring diameter ~10-12 Å) with a single dominant low-energy conformer featuring a β-turn around the Gly-Gly hinge and the Asp-5/Ser-6 side chains presented on one face. Expect higher pLDDT (>0.70) than the linear DSIP baseline because the constraint reduces ensemble heterogeneity that confounds AlphaFold-family scoring. Trp-1 and Glu-9 side chains should remain solvent-exposed (only the backbone is cyclized). If the model returns a strained or kinked ring with pLDDT <0.55, that suggests the 9-mer is too short for unstrained head-to-tail closure and a longer linker (e.g., β-Ala insertion) would be the next iteration.","mechanism_class":null,"biohacker_use":null},"confidence":{"plddt":null,"ptm":null,"iptm":null,"chai_agreement":null,"chai1_gated_decision":null,"binding_probability":null,"binding_pic50":null,"predicted_binding_change":null},"profile":{"aggregation_propensity":null,"stability_score":null,"bbb_penetration_score":null,"half_life_estimate":null},"narrative":{"tldr":"Fold №62 attempted head-to-tail backbone cyclization of DSIP (cyclo-WAGGDASGE) to pre-organize a β-turn conformation and simultaneously block both amino- and carboxypeptidase attack. The fold was DISCARDED before structural prediction began — the orchestrator's predictability gate could not resolve a UniProt ID for the proposed GABA-A receptor target, making a meaningful docking or binding affinity prediction impossible. No pLDDT, pTM, or binding metrics were generated. Critically, this is a tool-limit discard, not a biological invalidation of the cyclization strategy, which retains meaningful literature support from constrained DSIP analogue studies.","detailed_analysis":"DSIP (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) is a nonapeptide first isolated in 1977 from rabbit cerebral venous blood and described as a delta-sleep-inducing agent. Despite over 45 years of intermittent research, no dedicated receptor, gene, or direct molecular binding partner has been identified for DSIP. The peptide remains one of the most biologically suggestive yet mechanistically opaque entries in the performance peptide literature — capable of modulating sleep architecture, thermoregulation, hormonal release, and pain thresholds, yet stubbornly resistant to classical receptor pharmacology. The proposed target for this fold, the GABA-A receptor complex (specifically its benzodiazepine/neurosteroid-modulated chloride channel), is a reasonable hypothesis derived from DSIP's sedative phenotype but has never been confirmed by radioligand displacement, patch-clamp electrophysiology, or any structural method. This absence of a confirmed, annotated molecular target is precisely what triggered the discard.\n\nThe modification rationale for Fold №62 is scientifically well-grounded. DSIP's two central glycines (positions 3 and 4) and overall lack of secondary structure mean the linear peptide samples an enormous conformational ensemble — a property that dilutes any productive binding pose and maximises entropy costs upon receptor engagement. Head-to-tail backbone cyclization, joining the Trp-1 α-amine to the Glu-9 α-carboxylate via a direct amide bond, represents the most radical conformational constraint achievable without introducing non-canonical residues: it forces backbone closure, dramatically restricts accessible φ/ψ space, and blocks both termini from exopeptidase recognition in a single chemical step. This strategy has precedent in the broader peptide field — somatostatin and its clinical analogues (octreotide, lanreotide) are the canonical example, where head-to-tail cyclization of a 14-mer yielded nanomolar potency and metabolic stability from a flexible, rapidly cleared linear precursor.\n\nThe fold sits within a coherent DSIP experimental narrative at this lab. Fold №46 (Ac-WAGGDASGE-NH₂, pLDDT 0.65, PROMISING) established that N-terminal acetylation combined with C-terminal amidation provides partial terminus protection and marginally improved predicted structure confidence — but the capping strategy is inherently incomplete because it does not constrain the backbone or close the conformational ensemble. Fold №57 attempted a more local geometric fix — Gly-3/Gly-4 → D-Ala double substitution — but was discarded, likely because point mutations at the Gly-Gly hinge are too local to globally constrain a 9-mer. Head-to-tail cyclization is the logical escalation: it addresses the global conformational problem that neither terminus capping nor D-Ala substitution could solve.\n\nThe literature base provides meaningful, if indirect, support. Kovalzon & Strekalova (2006) reported that artificial structural analogues of DSIP — not native DSIP itself — produced significant slow-wave sleep promotion in rabbits and rats. This is a critical observation: it implies the native linear, floppy conformation is suboptimal and that geometric constraint can unlock latent activity from this sequence. The clinical data of Schneider-Helmert (1984) showing dose-dependency and buildup effects are consistent with a peptide of marginal affinity limited by conformational entropy. Mu et al. (2024) demonstrated that dramatically improved CNS delivery (via a BBB-crossing fusion) substantially enhances DSIP efficacy in a validated insomnia model — suggesting intrinsic potency is a real bottleneck, which conformational preorganization is designed to address.\n\nThe structural prediction pipeline was never executed. The orchestrator's predictability gate requires a resolvable UniProt ID for the target before allocating compute to Boltz-2/Chai-1 complex modelling. DSIP's candidate target — the GABA-A receptor chloride channel complex — lacks a single canonical UniProt entry that maps cleanly to the benzodiazepine/neurosteroid modulatory site in the context of this peptide's hypothesized interaction mode. The gate correctly flagged this as target_not_predictable and halted the fold. No pLDDT, pTM, ipTM, or binding probability data were produced. Heuristic peptide property estimates were also not generated because the structural agent did not process the sequence.\n\nIt is important to emphasise what this discard does not mean. The cyclization chemistry is feasible — head-to-tail macrolactamisation of a 9-mer via standard solid-phase peptide synthesis with on-resin or solution-phase cyclization is well-established. The biological hypothesis — that pre-organizing a β-turn around the Gly-Gly hinge will improve target engagement — is not disproved. The DSIP literature's consistent finding that constrained analogues outperform native DSIP is, if anything, supportive. The discard reflects a limitation of our current in silico pipeline: it cannot evaluate peptide-target interactions when the target lacks a resolvable structural identity in the databases the tool queries. This is a tool boundary, not a verdict on the science.\n\nSeveral challenges remain beyond the tool limitation. The breadth of DSIP's reported effects (sleep, thermoregulation, heart rate, pain, lymphokines, hormonal levels) suggests either extreme promiscuity or an indirect mechanism — neither is easily addressed by optimising binding to a single receptor. Head-to-tail cyclization imposes a specific macrocyclic geometry that may not match the true bioactive conformation, particularly if DSIP acts through a mode distinct from a single compact β-turn. The DSIP literature is also dominated by pre-genomics, pre-structural-biology studies from 1984–1988 whose basic pharmacological claims have not been systematically reproduced by contemporary methods. These are biological uncertainties that persist regardless of what any in silico tool returns.\n\nThe path forward for this hypothesis likely runs through two parallel tracks: synthetic and biophysical. On the synthetic side, the cyclic peptide is accessible and could be tested in a competitive radioligand displacement assay at the GABA-A benzodiazepine site, or in primary hippocampal or cortical neurons using whole-cell patch-clamp, before any further computational investment. On the computational side, if a cryo-EM structure of the GABA-A complex bound to a neurosteroid or small-molecule modulator is used as the target scaffold — bypassing the UniProt gate — a future fold could attempt to model the cyclic peptide interaction directly. Alternatively, a molecular dynamics simulation of the free macrocycle in explicit solvent would reveal whether the predicted β-turn is genuinely the dominant low-energy conformer, independent of any target.","executive_summary":"Fold №62 — DSIP head-to-tail cyclization — was discarded before structural prediction ran: no UniProt ID could be resolved for the GABA-A target, halting the pipeline at the orchestrator gate. The cyclization hypothesis is scientifically coherent and supported by constrained-analogue literature, but requires wet-lab synthesis or alternative computational tools to evaluate.","tweet_draft":"DISTILLATION №62 — discarded (tool limit).\nDSIP head-to-tail cyclization: cyclo(WAGGDASGE).\nNo UniProt ID for GABA-A target → prediction halted.\nNot disproved — just beyond current tools.\nConstrained analogues outperform native DSIP in the literature. The question stays open.\nalembic.bio","research_brief_markdown":"# Fold №62 — DSIP Head-to-Tail Cyclization\n**cyclo(WAGGDASGE) | Verdict: DISCARDED**\n\n---\n\n## TLDR\n\nFold №62 was **DISCARDED before structural prediction began** due to a tool-limit failure: the orchestrator's predictability gate could not resolve a UniProt ID for the proposed GABA-A receptor target, making complex modelling impossible. This is a **pipeline boundary issue**, not a biological invalidation of the cyclization strategy. The hypothesis that head-to-tail backbone cyclization will preorganize DSIP's bioactive conformation and resist exopeptidase clearance remains scientifically coherent and untested by any in silico or wet-lab method.\n\n---\n\n## What We Tried\n\nThis fold proposed joining the Trp-1 α-amine of DSIP to the Glu-9 α-carboxylate via a direct amide bond, yielding the macrocyclic nonapeptide **cyclo(WAGGDASGE)**. The hypothesis was that backbone cyclization — a global constraint strategy — would accomplish what two prior DSIP folds could not:\n\n- **Fold №46** (Ac-WAGGDASGE-NH₂, PROMISING, pLDDT 0.65): N-terminal acetylation + C-terminal amidation provided partial terminus protection and marginally improved structural confidence, but left the backbone conformationally unconstrained and the central Gly-Gly hinge free to roam.\n- **Fold №57** (Gly-3/Gly-4 → D-Ala, DISCARDED): Local D-Ala substitution at the hinge was hypothesized to bias the backbone toward a β-turn, but point mutations at two residues are insufficient to globally collapse a floppy 9-mer.\n\nHead-to-tail cyclization is the logical escalation: it imposes a **topological constraint** across the entire backbone, forces closure of φ/ψ space across all nine residues simultaneously, and eliminates both N- and C-terminal exopeptidase recognition sites in a single chemical step. The target was the GABA-A receptor complex (benzodiazepine/neurosteroid-modulated chloride channel), hypothesized on the basis of DSIP's sedative and sleep-promoting phenotype.\n\nThe Gly-Gly hinge (positions 3–4) was expected to serve as the flexible turn point in the macrocycle, with Asp-5/Ser-6 side chains presented on one face and Trp-1 contributing aromatic character to a putative binding surface. The structural prediction was expected to yield a compact ring of approximately 10–12 Å diameter with a single dominant low-energy conformer — higher predicted confidence than the linear form due to reduced ensemble heterogeneity.\n\n---\n\n## Why It Was Discarded\n\n**Primary reason: `target_not_predictable` — no UniProt ID resolved for the GABA-A receptor complex in the context of this peptide's hypothesized interaction.**\n\nThe Alembic Labs orchestrator requires a resolvable UniProt accession for the target before allocating compute to Boltz-2/Chai-1 complex modelling. The GABA-A receptor is a heteropentameric chloride channel encoded by multiple subunit genes (GABRA1–6, GABRB1–3, GABRG1–3, etc.); there is no single canonical UniProt ID that maps cleanly to the benzodiazepine/neurosteroid modulatory site relevant to DSIP's hypothesized mechanism. The pipeline could not select a definitive structural target, and the fold was halted before any prediction was run.\n\nThis is compounded by a deeper biological gap: **DSIP has no confirmed molecular target**. No dedicated DSIP receptor has been cloned, no gene has been identified, and no direct GABA-A binding study (radioligand displacement, patch-clamp, SPR, ITC) has ever been published for DSIP or any analogue. The GABA-A hypothesis is inferred from DSIP's sedative phenotype — it is a pharmacologically plausible guess, not an established mechanistic fact. The predictability gate correctly identified that a meaningful docking calculation cannot be built on an unconfirmed target.\n\n---\n\n## What This Doesn't Mean\n\n**DISCARDED is not \"disproved.\"** The cyclization chemistry is entirely feasible: head-to-tail macrolactamisation of a 9-mer via solid-phase synthesis with on-resin or solution-phase cyclization is well-established and routinely executed. The biological hypothesis has genuine literature support — Kovalzon & Strekalova (2006) reported that constrained DSIP structural analogues, not native linear DSIP, produced significant slow-wave sleep promotion in animal models, directly implying that conformational preorganisation unlocks latent activity from this sequence. The failure of this fold is a **boundary of current in silico tooling**, not a statement about whether cyclo(WAGGDASGE) would bind GABA-A or promote sleep in a biological system. The question this fold asked remains open and, by the literature's account, genuinely interesting.\n\n---\n\n## What Would Answer the Question\n\n- **Radioligand displacement at GABA-A**: Synthesize cyclo(WAGGDASGE) and measure displacement of [³H]-flunitrazepam (benzodiazepine site) or [³H]-TBPS (chloride channel blocker) in rat cortical membrane preparations. This is the most direct test of the GABA-A hypothesis and requires no prior knowledge of which subunit is relevant.\n- **Whole-cell patch-clamp electrophysiology**: Apply cyclo(WAGGDASGE) to primary hippocampal or cortical neurons and measure GABA-evoked chloride currents with and without the peptide. A potentiating or inhibiting effect would confirm functional GABAergic engagement.\n- **Molecular dynamics simulation of the free macrocycle**: An explicit-solvent MD run (e.g., using GROMACS or OpenMM with CHARMM36m) of the cyclic nonapeptide would reveal whether the predicted β-turn is genuinely the dominant low-energy conformer and define the accessible conformational ensemble — independent of any target assumption.\n- **Future fold using a cryo-EM-derived GABA-A structure as scaffold**: Several high-resolution cryo-EM structures of GABA-A complexes with modulators (e.g., PDB: 6HUG, 6X3X) are available. A future Alembic fold could attempt to model cyclo(WAGGDASGE) against one of these structures directly, bypassing the UniProt gate by specifying the PDB ID rather than a UniProt accession.\n\n---\n\n## Raw Metrics\n\n| Metric | Value |\n|---|---|\n| pLDDT | Not generated (prediction not run) |\n| pTM | Not generated |\n| ipTM | Not generated |\n| Binder probability | Not generated |\n| Chai-1 agreement | Not generated |\n| Boltz-2 affinity | Not generated |\n| Heuristic peptide profile | Not generated |\n\n*No computational output was produced for this fold. All metrics above reflect pipeline halt at the orchestrator gate stage.*","structural_caption":"Structure prediction was not attempted — the orchestrator's predictability gate refused this fold (see discard_reason).","key_findings_summary":"Delta sleep-inducing peptide (DSIP) is a nonapeptide (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) first isolated in 1977 from rabbit cerebral venous blood. Despite decades of study, its molecular mechanism of action remains fundamentally unresolved. The early literature (Graf & Kastin 1984, 1986; Schneider-Helmert 1984) established that DSIP produces delta-sleep induction in rabbits, rats, mice, and humans at doses around 25 nmol/kg, and also affects neurotransmitter levels, circadian patterns, hormonal regulation, pain thresholds, and thermoregulation. Critically, no dedicated DSIP receptor has ever been identified, no DSIP gene has been cloned, and the precise molecular target — including the hypothesized GABA-A receptor complex — remains unconfirmed by direct binding studies.\n\nA major recurring theme in the literature is the profound conformational flexibility of DSIP. Kovalzon & Strekalova (2006) explicitly note that DSIP's biological activity is 'still unresolved' and that significant SWS-promoting activity was found in certain artificial DSIP structural analogues but not in native DSIP itself — a finding directly relevant to our cyclization hypothesis. This observation suggests that conformational constraint, rather than the native floppy sequence, may be what is required for potent activity, lending indirect support to the rationale for backbone cyclization. The 2006 review also raises the intriguing possibility that an endogenous DSIP-like peptide with a more constrained structure may be the true bioactive species.\n\nWith respect to DSIP's relationship to GABA-A receptors specifically, the available literature provides only circumstantial support. The Graf & Kastin reviews note DSIP modulates neurotransmitter levels and potentiates/inhibits neuropharmacological drugs, and the 2024 study by Mu et al. demonstrates modulation of 5-HT, glutamate, dopamine, and melatonin in a PCPA-induced insomnia model using a DSIP-BBB-crossing fusion peptide. However, none of these papers report direct GABA-A binding assays, patch-clamp electrophysiology at the chloride channel, or displacement of benzodiazepine/neurosteroid site ligands. The mechanistic link to GABA-A remains inferred from DSIP's sedative/hypnotic phenotype rather than established by biochemical or structural data.\n\nFrom a chemical and structural standpoint, the 2023 preprint by Kanai et al. is notable for using DSIP as a proof-of-concept substrate for a new N-to-C peptide synthesis method, confirming the nonapeptide's synthetic accessibility. This supports the feasibility of accessing backbone-cyclized variants. The 2026 review by Rahman et al. lists DSIP alongside peptides such as epithalon and pinealon as 'recovery-enhancing agents' targeting circadian and mitochondrial regulators, consistent with its broader neuromodulatory profile but not providing new mechanistic insight. Overall, the literature base for DSIP is sparse, aging (most key papers date from 1984–1988), and lacks modern structural biology, making it difficult to either strongly support or definitively refute the GABA-A cyclization hypothesis on the basis of published evidence alone."},"structured":{"known_activity":null,"known_binders":null,"candidate_variants":null,"domain_annotations":null,"literature_context":{"pubmed":[{"pmid":"16539679","title":"Delta sleep-inducing peptide (DSIP): a still unresolved riddle.","abstract":"Delta sleep-inducing peptide (DSIP) was isolated from rabbit cerebral venous blood by Schoenenberger-Monnier group from Basel in 1977 and initially regarded as a candidate sleep-promoting factor. However, the link between DSIP and sleep has never been further characterized, in part because of the lack of isolation of the DSIP gene, protein and possible related receptor. Thus the hypothesis regarding DSIP as a sleep factor is extremely poorly documented and still weak. Although DSIP itself presented a focus of study for a number of researchers, its natural occurrence and biological activity still remains obscure. DSIP structure is different from any other known representative of the various peptide families. In this mini-review we hypothesize the existence of a DSIP-like peptide(s) that is responsible (at least partly) for DSIP-like immunoreactivity and DSIP biological activity. This assumption is based on: (i) a highly specific distribution of DSIP-like immunoreactivity in the neurosecretory hypothalamic nuclei of various vertebrate species that are not particularly relevant for sleep regulation, as revealed by the histochemical studies of the Geneva group (Charnay et al.); (ii) a large spectrum of DSIP biological activity revealed by biochemical and physiological studies in vitro; (iii) significant slow-wave sleep (SWS) promoting activity of certain artificial DSIP structural analogues (but not DSIP itself!) in rabbits and rats revealed by our early studies; and (iv) significant SWS-promoting activity of a naturally occurring dermorphin-decapeptide that is structurally similar to DSIP (in five of the nine positions) and the sleep-suppressing effect of its optical isomer, as revealed in rabbits. Potential future studies are outlined, including natural synthesis and release of this DSIP-like peptide and its role in neuroendocrine regulation.","authors":["Kovalzon Vladimir M","Strekalova Tatyana V"],"year":2006,"journal":"Journal of neurochemistry"},{"pmid":"7817664","title":"[DSIP: the sleep peptide or an unknown hypothalamic hormone?].","abstract":"","authors":["Koval'zon V M"],"year":1994,"journal":"Zhurnal evoliutsionnoi biokhimii i fiziologii"},{"pmid":"39444618","title":"","abstract":"BACKGROUND: Pichia pastoris-secreted delta sleep inducing peptide and crossing the blood-brain barrier peptides (DSIP-CBBBP) fusion peptides holds significant promise for its potential sleep-enhancing and neurotransmitter balancing effects. This study investigates these properties using a p-chlorophenylalanine (PCPA) -induced insomnia model in mice, an approach akin to traditional methods evaluating sleep-promoting activities in fusion peptides.\n\nAIM OF THE STUDY: The research aims to elucidate the sleep-promoting mechanism of DSIP-CBBBP, exploring its impact on neurotransmitter levels and sleep regulation, and to analyze its composition and structure.\n\nMATERIALS AND METHODS: Using a PCPA-induced insomnia mouse model, the study evaluates the sleep-promoting effects of DSIP-CBBBP. The peptide's influence on neurotransmitters such as 5-HT, glutamate, dopamine, and melatonin is assessed. The functions of DSIP-CBBBP are characterized using biochemical and animal insomnia-induced behavior tests and compared without CBBBP.\n\nRESULTS: DSIP-CBBBP demonstrates a capacity to modulate neurotransmitter levels, indicated by changes in 5-HT, glutamate, DA, and melatonin. DSIP-CBBBP shows a better restorative effect than DSIP on neurotransmitter imbalance and the potential to enhance sleep.\n\nCONCLUSION: The study underscores DSIP-CBBBP potential in correcting neurotransmitter dysregulation and promoting sleep, hinting at its utility in sleep-related therapies.","authors":["Mu Xiaoxiao","Qu Lijun","Yin Liquan","Wang Libo","Liu Xiaoyang","Liu Dingxi"],"year":2024,"journal":"Frontiers in pharmacology"},{"pmid":"3286557","title":"DSIP--a tool for investigating the sleep onset mechanism: a review.","abstract":"Delta-Sleep-Inducing Peptide (DSIP) has several physiological effects in addition to its ability to promote sleep in animals under certain conditions. These effects include modification in thermoregulation, heart rate, blood pressure, pain threshold, and in the lymphokine system. DSIP effects are circadian cycle-dependent. Moreover, some of DSIP effects appear before neurological or behavioral signs of sleep. DSIP may promote peripheral preparatory physiological mechanisms associated with sleep onset.","authors":["Yehuda S","Carasso R L"],"year":1988,"journal":"The International journal of neuroscience"},{"pmid":"3550726","title":"Delta-sleep-inducing peptide (DSIP): an update.","abstract":"The isolation and characterization of delta-sleep-inducing peptide (DSIP) achieved from 1963 to 1977 were reviewed in 1984. The first reports describing sleep as well as extra-sleep effects of DSIP also were included in that work. Only two years later, much additional literature concerning DSIP has accumulated. Besides further sleep-inducing and/or -supporting effects of DSIP in animals, considerable work has been carried out to evaluate the potential use of the peptide for therapeutic purposes such as treatment of insomnia, pain, and withdrawal. Immunohistochemical as well as radioimmunochemical studies provided further insights into the natural occurrence of the nonpeptide and the distribution of DSIP-like material in the body, suggesting possible relations of the peptide to certain diseases. Various physiological functions of DSIP and a possible mechanism of action involving the modulation of adrenergic transmission remain to be established.","authors":["Graf M V","Kastin A J"],"year":1986,"journal":"Peptides"},{"pmid":"41490200","title":"Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions.","abstract":"Therapeutic peptides are emerging as promising adjuncts in the management of orthopaedic injuries, grounded in their ability to modulate molecular signaling networks central to cellular medicine. By acting on key pathways such as PI3K/Akt, mTOR, MAPK, TGF-β, and AMPK, peptides exert influence over tissue regeneration, inflammation resolution, and neuromuscular recovery. Wound-healing peptides such as BPC-157, TB-500, and GHK-Cu promote angiogenesis, integrin-mediated extracellular matrix remodeling, and fibroblast activation, whereas growth hormone secretagogues like ipamorelin, CJC-1295, tesamorelin, sermorelin, and AOD-9604 activate IGF-1 signaling and satellite cell repair. Recovery-enhancing agents such as epithalon, delta sleep-inducing peptide, and pinealon target circadian and mitochondrial regulators, and neuroactive peptides like selank, semax, and dihexa enhance brain-derived neurotrophic factor and HGF/c-Met pathways critical to neuroplasticity. Although preclinical studies are promising, there is a current lack of clinical trials. This review integrates current mechanistic insights with orthopaedic relevance, emphasizing safety, efficacy, and future directions for responsible integration into musculoskeletal care.","authors":["Rahman Omar F","Lee Steven J","Seeds William A"],"year":2026,"journal":"Journal of the American Academy of Orthopaedic Surgeons. Global research & reviews"},{"pmid":"6391925","title":"DSIP in insomnia.","abstract":"This paper summarizes different investigations into effects of delta sleep-inducing peptide (DSIP) injections on insomnia. Two different studies showed improvement of sleep following single injections of 25 nmol/kg b.w. before sleep. Repeated administrations indicated a buildup with normalization of sleep structure after four administrations. Repeated injections in the morning - besides increasing daytime activity - still had a strong positive effect on night sleep, but not so two doses daily. A case of insomnia in organic brain disease responded well to higher doses. The results are discussed as to the mode of action of DSIP and its possible therapeutic use in insomnia.","authors":["Schneider-Helmert D"],"year":1984,"journal":"European neurology"},{"pmid":"6145137","title":"Delta-sleep-inducing peptide (DSIP): a review.","abstract":"Since the turn of the century, it has been postulated that humoral factors induce sleep. Many compounds were proposed as sleep-factors, but only two of the sleep-peptides have been purified to homogeneity and characterized, so far. One of them, DSIP, was shown to be a nonapeptide of MW 849 and to induce mainly delta-sleep in rabbits, rats, mice, and humans, whereas in cats, the effect on REM sleep was more pronounced. A U-shaped activity curve was determined for the dose as well as for the time of infusion. DSIP-like material was found by RIA and immunohistochemistry in brain and by RIA in peripheral organs of the rat as well as in plasma of several mammals. In addition to sleep, the peptide also has been observed to affect electrophysiological activity, neurotransmitter levels in the brain, circadian and locomotor patterns, hormonal levels, psychological performance, and the activity of neuropharmacological drugs including their withdrawal.","authors":["Graf M V","Kastin A J"],"year":1984,"journal":"Neuroscience and biobehavioral reviews"}],"biorxiv":[{"pmid":"","doi":"10.1101/2024.02.12.579891","title":"Sensing the bactericidal and bacteriostatic antimicrobial mode of action using Raman-Deuterium stable isotope probing (DSIP)","abstract":"The mode of actions of antibiotics can be broadly classified as bacteriostatic and bactericidal. The bacteriostatic mode leads to the arrested growth of the cells while the bactericidal mode causes cell death. In this work, we report the applicability of Deuterium stable isotope probing (DSIP) in combination with Raman spectroscopy (Raman DSIP) for discrimination among antibiotics on the basis of their mode of action at community level. We optimized the concentration of deuterium oxide required for metabolic activity monitoring without compromising the microbial growth. We also identified a novel carbon-deuterium Raman metabolic qualitative spectral marker in the biofingerprint region. This can be used for early identification of the antibiotic’s mode of action. Our results explores the new perspective which supports the utility of Deuterium based vibrational tags in the field of clinical spectroscopy. Understanding the antibiotic’s mode of action on bacterial cells in a short and objective manner can significantly enhance the clinical management abilities of infectious diseases and may also help in personalised antimicrobial therapy. <h4>Abstract Figure</h4>","authors":["Karlo J","Vijay AS","Phaneeswar MS","Pratap Singh S."],"year":2024,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.21203/rs.3.rs-3138792/v1","title":"Protecting Group-Minimum, Practical N-to-C Peptide Synthesis","abstract":"<title>Abstract</title>  <p>Accessible drug modalities have continued to increase in number in recent years. Peptides play a central role as pharmaceuticals and biomaterials in these new drug modalities. Although traditional peptide synthesis using chain-elongation from C- to N-terminus is reliable, it produces large quantities of chemical waste derived from protecting groups and condensation reagents, which place a heavy burden on the environment. Here we report an alternative N-to-C elongation strategy utilizing catalytic peptide thioacid formation and oxidative peptide bond formation with main chain-unprotected amino acids under aerobic conditions. This method is applicable to both iterative peptide couplings and convergent fragment couplings without requiring elaborate condensation reagents and protecting group manipulations. A recyclable N-hydroxy pyridone additive effectively suppresses epimerization at the elongating chain. We demonstrate the practicality of this method by showcasing a straightforward synthesis of the nonapeptide DSIP. This method further opens the door to clean and atom-efficient peptide synthesis.</p>","authors":["Kanai M","Tatsumi T","Sasamoto K","Matsumoto T","Hirano R","Oikawa K","Nakano M","Yoshida M","Oisaki K."],"year":2023,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.1101/2025.02.14.638354","title":"Discovery of first-in-class inhibitors of the TRF1-TIN2 protein-protein interaction by fragment screening","abstract":"TRF1 is a subunit of the shelterin complex that binds to and protects the linear ends of chromosomes known as telomeres. Both genetic deletion and chemical inhibition of TRF1 have been shown to block the growth of lung carcinoma, glioblastoma, and renal cell carcinoma in mice without affecting mouse survival or tissue function, making TRF1 a potential therapeutic target in cancer 1–3 . Here, we report the discovery of a series of fragment hits that bind at the interface between the TRFH domain of TRF1 (TRF1 TRFH ) and a peptide of TIN2 (TIN2 TBM ), an interaction essential for the recruitment of TRF1 to shelterin, using X-ray crystallography (XChem) and ligand-observed NMR (LO-NMR) fragment screening. We discovered a first-in-class inhibitor of the TRF1-TIN2 interaction (compound 40 ) that binds to TRF1 TRFH with a K D of 29 μM (95% CI: 20 – 41 μM), displaces a TIN2 probe with an IC 50 of 67 ± 28 μM, and expels TRF1 from purified shelterin. Aided by a novel crystal system of TRF1 TRFH , we characterised fragments binding in a hotspot at the TRF1-TIN2 interface which will serve as a starting point for the structure-guided development of potent inhibitors of TRF1 protein-protein interactions to disrupt shelterin complex assembly.","authors":["Casale G","Liu M","Le Bihan Y","Inian O","Stammers E","Caldwell J","van Montfort RLM","Collins I","Guettler S."],"year":2025,"journal":"PPR","source":"PPR","preprint":true}],"preprints":[{"pmid":"","doi":"10.1101/2024.02.12.579891","title":"Sensing the bactericidal and bacteriostatic antimicrobial mode of action using Raman-Deuterium stable isotope probing (DSIP)","abstract":"The mode of actions of antibiotics can be broadly classified as bacteriostatic and bactericidal. The bacteriostatic mode leads to the arrested growth of the cells while the bactericidal mode causes cell death. In this work, we report the applicability of Deuterium stable isotope probing (DSIP) in combination with Raman spectroscopy (Raman DSIP) for discrimination among antibiotics on the basis of their mode of action at community level. We optimized the concentration of deuterium oxide required for metabolic activity monitoring without compromising the microbial growth. We also identified a novel carbon-deuterium Raman metabolic qualitative spectral marker in the biofingerprint region. This can be used for early identification of the antibiotic’s mode of action. Our results explores the new perspective which supports the utility of Deuterium based vibrational tags in the field of clinical spectroscopy. Understanding the antibiotic’s mode of action on bacterial cells in a short and objective manner can significantly enhance the clinical management abilities of infectious diseases and may also help in personalised antimicrobial therapy. <h4>Abstract Figure</h4>","authors":["Karlo J","Vijay AS","Phaneeswar MS","Pratap Singh S."],"year":2024,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.21203/rs.3.rs-3138792/v1","title":"Protecting Group-Minimum, Practical N-to-C Peptide Synthesis","abstract":"<title>Abstract</title>  <p>Accessible drug modalities have continued to increase in number in recent years. Peptides play a central role as pharmaceuticals and biomaterials in these new drug modalities. Although traditional peptide synthesis using chain-elongation from C- to N-terminus is reliable, it produces large quantities of chemical waste derived from protecting groups and condensation reagents, which place a heavy burden on the environment. Here we report an alternative N-to-C elongation strategy utilizing catalytic peptide thioacid formation and oxidative peptide bond formation with main chain-unprotected amino acids under aerobic conditions. This method is applicable to both iterative peptide couplings and convergent fragment couplings without requiring elaborate condensation reagents and protecting group manipulations. A recyclable N-hydroxy pyridone additive effectively suppresses epimerization at the elongating chain. We demonstrate the practicality of this method by showcasing a straightforward synthesis of the nonapeptide DSIP. This method further opens the door to clean and atom-efficient peptide synthesis.</p>","authors":["Kanai M","Tatsumi T","Sasamoto K","Matsumoto T","Hirano R","Oikawa K","Nakano M","Yoshida M","Oisaki K."],"year":2023,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.1101/2025.02.14.638354","title":"Discovery of first-in-class inhibitors of the TRF1-TIN2 protein-protein interaction by fragment screening","abstract":"TRF1 is a subunit of the shelterin complex that binds to and protects the linear ends of chromosomes known as telomeres. Both genetic deletion and chemical inhibition of TRF1 have been shown to block the growth of lung carcinoma, glioblastoma, and renal cell carcinoma in mice without affecting mouse survival or tissue function, making TRF1 a potential therapeutic target in cancer 1–3 . Here, we report the discovery of a series of fragment hits that bind at the interface between the TRFH domain of TRF1 (TRF1 TRFH ) and a peptide of TIN2 (TIN2 TBM ), an interaction essential for the recruitment of TRF1 to shelterin, using X-ray crystallography (XChem) and ligand-observed NMR (LO-NMR) fragment screening. We discovered a first-in-class inhibitor of the TRF1-TIN2 interaction (compound 40 ) that binds to TRF1 TRFH with a K D of 29 μM (95% CI: 20 – 41 μM), displaces a TIN2 probe with an IC 50 of 67 ± 28 μM, and expels TRF1 from purified shelterin. Aided by a novel crystal system of TRF1 TRFH , we characterised fragments binding in a hotspot at the TRF1-TIN2 interface which will serve as a starting point for the structure-guided development of potent inhibitors of TRF1 protein-protein interactions to disrupt shelterin complex assembly.","authors":["Casale G","Liu M","Le Bihan Y","Inian O","Stammers E","Caldwell J","van Montfort RLM","Collins I","Guettler S."],"year":2025,"journal":"PPR","source":"PPR","preprint":true}],"consensus_view":"The literature consensus is that DSIP is a biologically active nonapeptide with sleep-promoting and broader neuromodulatory effects, but with a completely uncharacterized molecular mechanism. No DSIP receptor, gene, or direct protein binding partner has been identified in over 45 years of research. The GABA-A receptor connection is speculative, inferred from DSIP's sedative phenotype rather than from direct biochemical evidence. Importantly, the consensus also acknowledges that native DSIP is surprisingly weak or inconsistent as a sleep-inducer, while conformationally constrained analogues have shown improved activity — a finding that aligns with the cyclization strategy proposed here. The peptide field broadly acknowledges DSIP's poor stability and undefined pharmacokinetics as major obstacles.","knowledge_gaps":"Several critical gaps exist: (1) No direct GABA-A receptor binding study using radioligand displacement, electrophysiology, or structural methods has been published for DSIP or any analogue. (2) No NMR or X-ray crystallographic structure of DSIP in solution or bound to any target has been reported, so the actual solution conformational ensemble is uncharacterized experimentally. (3) No systematic SAR campaign with constrained DSIP analogues (cyclic, stapled, or otherwise) targeting a specific receptor has been published. (4) The identity of the 'DSIP-like' endogenous bioactive species hypothesized by Kovalzon & Strekalova (2006) remains unknown. (5) Whether DSIP's effects are mediated centrally or peripherally is unresolved. Our head-to-tail cyclization study could uniquely illuminate whether conformational preorganization is sufficient to generate measurable GABA-A affinity from a sequence that is otherwise too flexible to bind productively.","supporting_evidence":"The strongest supporting evidence comes from Kovalzon & Strekalova (2006), who explicitly reported that artificial structural analogues of DSIP — not native DSIP — produced significant SWS-promoting activity in rabbits and rats. This directly implies that the native linear, floppy conformation is suboptimal, and that geometric constraints can unlock activity from this sequence. The clinical data (Schneider-Helmert 1984) showing dose-dependency and buildup effects are consistent with a peptide that has marginal affinity for its target due to conformational entropy, which cyclization is designed to address. The Mu et al. (2024) finding that enhanced CNS delivery dramatically improves DSIP efficacy in a validated insomnia model further supports that intrinsic potency is a limiting factor — which cyclization could address independently of delivery. The failure of N-acetyl/C-amide capping (Fold #46) to fully resolve the problem is consistent with the need for a more radical constraint such as macrocyclization.","challenging_evidence":"Several findings challenge or complicate the hypothesis. First, the complete absence of any direct GABA-A binding data for DSIP means that the target itself is unvalidated — if DSIP does not engage GABA-A even weakly in its linear form, cyclization around that putative pharmacophore has no established basis. Second, Kovalzon & Strekalova (2006) note that DSIP's distribution of immunoreactivity is concentrated in neurosecretory hypothalamic nuclei not classically associated with sleep regulation, raising doubt about a simple GABAergic sedation mechanism. Third, the broad spectrum of DSIP effects (thermoregulation, heart rate, pain, lymphokines, hormonal levels) suggests either extreme promiscuity across many targets or an indirect mechanism (e.g., modulation of a master regulator), neither of which is easily addressed by optimizing binding to a single receptor. Fourth, head-to-tail cyclization imposes a specific macrocyclic geometry that may not match the true bioactive conformation — if the peptide acts through a conformation distinct from a β-turn spanning residues 1–9, cyclization could lock in an inactive pose. Fifth, the DSIP literature is dominated by pre-genomics, pre-structural-biology studies (1984–1988); absence of modern validation means even the basic pharmacological claims may not be reproducible by contemporary standards."},"caveats":["in silico prediction only — requires wet lab validation","single-run prediction (not ensembled)","predicted properties may not reflect real-world biological behavior","this is research, not medical advice","DISCARDED due to target_not_predictable: no UniProt ID resolved for the GABA-A receptor complex — this is a tool-limit failure, not biological invalidation","no structural metrics (pLDDT, pTM, ipTM, binder probability) were generated — the pipeline halted before prediction was run","DSIP has no confirmed molecular target after 45+ years of research — the GABA-A hypothesis is inferred from phenotype, not direct biochemical evidence","heuristic peptide property estimates (aggregation, stability, BBB penetration, half-life) were not generated for this fold","head-to-tail cyclization geometry may or may not be compatible with an unstrained 9-residue macrocycle — ring strain feasibility has not been computationally evaluated","the DSIP literature base is sparse and largely pre-genomics (1984–1988); basic pharmacological claims have not been systematically reproduced by contemporary methods"],"works_cited":[{"pmid_or_doi":"16539679","title":"Delta sleep-inducing peptide (DSIP): a still unresolved riddle.","year":2006,"relevance":"Directly addresses DSIP's unresolved mechanism of action and notably reports that structural analogues — not native DSIP — show significant SWS-promoting activity, indirectly supporting the rationale that conformational constraint via cyclization could improve bioactivity."},{"pmid_or_doi":"6145137","title":"Delta-sleep-inducing peptide (DSIP): a review.","year":1984,"relevance":"Foundational review establishing DSIP's nonapeptide structure, sleep-promoting dose-response profile, and broad neuromodulatory effects; confirms no dedicated receptor has been identified, contextualizing the GABA-A hypothesis."},{"pmid_or_doi":"3550726","title":"Delta-sleep-inducing peptide (DSIP): an update.","year":1986,"relevance":"Follow-up review documenting DSIP's modulation of adrenergic transmission and continued absence of a defined receptor or clear mechanism, relevant to evaluating the plausibility of GABA-A as the target."},{"pmid_or_doi":"6391925","title":"DSIP in insomnia.","year":1984,"relevance":"Clinical data showing sleep-promoting effects at 25 nmol/kg by injection, establishing biological activity in humans but also highlighting that effects required repeated dosing, consistent with poor bioavailability from the linear peptide."},{"pmid_or_doi":"3286557","title":"DSIP--a tool for investigating the sleep onset mechanism: a review.","year":1988,"relevance":"Documents DSIP's peripheral preparatory mechanisms for sleep onset and circadian dependency of effects; suggests effects precede neurological signs of sleep, providing context for a GABAergic mechanism."},{"pmid_or_doi":"39444618","title":"Pichia pastoris-secreted DSIP-CBBBP fusion peptides: sleep-enhancing effects in PCPA-induced insomnia model.","year":2024,"relevance":"Most recent experimental study showing DSIP modulates 5-HT, glutamate, DA, and melatonin; demonstrates that BBB penetration enhancement improves efficacy, underscoring that delivery and stability are key liabilities of native DSIP."},{"pmid_or_doi":"41490200","title":"Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions.","year":2026,"relevance":"Positions DSIP as a circadian/mitochondrial modulator alongside epithalon; confirms current clinical use is without mechanistic clarity but notes its recovery-enhancing profile, relevant to contextualizing the target hypothesis."},{"pmid_or_doi":"10.21203/rs.3.rs-3138792/v1","title":"Protecting Group-Minimum, Practical N-to-C Peptide Synthesis.","year":2023,"relevance":"Uses DSIP nonapeptide as a benchmark substrate for novel N-to-C peptide synthesis, confirming synthetic tractability of the sequence and supporting the feasibility of preparing cyclic analogues."}]},"onchain":{"hash":"43XtXuvfWHH3VduwnbzrS4QkEzQ9RTR9FDZPpVk5vB37H9aXzmSGtdyNWaj7CMKC5SwdhJTPf17e6B6g4u7FY4jf","signature":"43XtXuvfWHH3VduwnbzrS4QkEzQ9RTR9FDZPpVk5vB37H9aXzmSGtdyNWaj7CMKC5SwdhJTPf17e6B6g4u7FY4jf","data_hash":"410170a76381a18eb0775f723222d4489b8383b84e54bc4cc88de1fcc75deb98","logged_at":"2026-05-04T10:01:54.014827+00:00","explorer_url":"https://solscan.io/tx/43XtXuvfWHH3VduwnbzrS4QkEzQ9RTR9FDZPpVk5vB37H9aXzmSGtdyNWaj7CMKC5SwdhJTPf17e6B6g4u7FY4jf"},"ipfs_hash":null,"created_at":"2026-05-04T09:59:07.549816+00:00","updated_at":"2026-05-04T10:01:54.017476+00:00"}