{"uniprot":"P08218","gene":"CELA2B","name":"Chymotrypsin-like elastase family member 2B","organism":"Homo sapiens (Human)","status":"dark","length":269,"sequence":"MIRTLLLSTLVAGALSCGVSTYAPDMSRMLGGEEARPNSWPWQVSLQYSSNGQWYHTCGGSLIANSWVLTAAHCISSSGIYRVMLGQHNLYVAESGSLAVSVSKIVVHKDWNSDQVSKGNDIALLKLANPVSLTDKIQLACLPPAGTILPNNYPCYVTGWGRLQTNGALPDDLKQGQLLVVDYATCSSSGWWGSTVKTNMICAGGDGVICTCNGDSGGPLNCQASDGRWEVHGIGSLTSVLGCNYYYKPSIFTRVSNYNDWINSVIANN","function_summary":"A secreted human serine endopeptidase that operates in the extracellular space to remodel protein substrates through elastase-like cleavage. Produced as a zymogen and activated outside the cell, it uses a canonical catalytic triad to drive proteolysis that shapes extracellular protein turnover. By tuning the proteolytic environment, it influences hormone-associated pathways, including insulin handling and secretion, and modulates platelet responses. Its activity is governed by tight associations with substrates and inhibitors that focus its action in extracellular niches.","plain_language":"CELA2B has barely been studied. The model's best guess: A secreted human serine endopeptidase that operates in the extracellular space to remodel protein substrates through elastase-like cleavage. Produced as a zymogen and activated outside the cell, it uses a canonical catalytic triad to drive proteolysis that shapes extracellular protein turnover.","uniprot_summary":"Serine-type endopeptidase.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:1901142","label":"insulin metabolic process"},{"id":"GO:0030155","label":"regulation of cell adhesion"},{"id":"GO:0050865","label":"regulation of cell activation"},{"id":"GO:0050708","label":"regulation of protein secretion"},{"id":"GO:0030163","label":"protein catabolic process"},{"id":"GO:0090330","label":"regulation of platelet aggregation"},{"id":"GO:0050796","label":"regulation of insulin secretion"},{"id":"GO:0032868","label":"response to insulin"}],"cellular_component":[{"id":"GO:0005576","label":"extracellular region"}]},"interpro":[{"id":"IPR009003","name":"Peptidase S1, PA clan","type":"homologous_superfamily","start":14,"end":268},{"id":"IPR001254","name":"Serine proteases, trypsin domain","type":"domain","start":28,"end":267},{"id":"IPR050850","name":"Peptidase S1 family, Elastase subfamily","type":"family","start":5,"end":266},{"id":"IPR001314","name":"Peptidase S1A, chymotrypsin family","type":"family","start":59,"end":74},{"id":"IPR001314","name":"Peptidase S1A, chymotrypsin family","type":"family","start":117,"end":131},{"id":"IPR001314","name":"Peptidase S1A, chymotrypsin family","type":"family","start":209,"end":221},{"id":"IPR018114","name":"Serine protease-like, trypsin family, histidine active site","type":"active_site","start":69,"end":74},{"id":"IPR033116","name":"Serine proteases, trypsin family, serine active site","type":"active_site","start":210,"end":221}],"reasoning":"I begin with the InterPro architecture. The core scaffold is IPR009003 (Peptidase S1, PA clan homologous superfamily, residues 14–268), which defines the double β-barrel fold characteristic of PA-clan serine endopeptidases. Nested within this scaffold is IPR001254 (Serine proteases, trypsin domain, residues 28–267), establishing the catalytic framework of the trypsin/chymotrypsin family. Multiple family-level signatures reinforce this identity: IPR050850 (Peptidase S1 family, Elastase subfamily, residues 5–266) and IPR001314 (Peptidase S1A, chymotrypsin family, residues 59–74, 117–131, 209–221) collectively map across the canonical S1A architecture. Two catalytic-site annotations pinpoint the charge-relay system: IPR018114 marks the histidine active site at residues 69–74, and IPR033116 marks the serine nucleophile at residues 210–221. Together, these features specify a secreted S1A serine endopeptidase that uses a His-Asp-Ser catalytic triad and an elastase-like substrate-binding pocket to cleave peptide bonds.\n\nThis domain layout causally dictates molecular function. The trypsin domain and S1A family signatures encode a serine-hydrolase mechanism that performs endoproteolysis; the elastase subfamily membership biases specificity toward small hydrophobic residues, a hallmark of elastase-like proteolysis. The presence of broad interaction surfaces typical of S1A proteases supports auxiliary protein binding, aligning with GO:0005515 protein binding as an inherent property of zymogen activation, inhibitor binding, and substrate capture.\n\nFrom this catalytic base, I infer the biological processes governed by extracellular proteolysis. Proteolytic cleavage of secreted and cell-surface substrates constitutes GO:0030163 protein catabolic process. In endocrine contexts, secreted serine proteases remodel peptide hormone milieus and insulin-containing granules; thus elastase-like cleavage can modulate hormone availability and secretion dynamics, fitting GO:1901142 insulin metabolic process and GO:0050796 regulation of insulin secretion, and aligning with GO:0032868 response to insulin through pathway tuning rather than direct hormone binding. In hemostasis and vascular biology, extracellular proteolysis alters matrix-bound cues and platelet receptor landscapes, providing a mechanistic route to GO:0090330 regulation of platelet aggregation.\n\nThe cellular component follows directly from secretion signals and the absence of intracellular retention motifs: this enzyme is synthesized as a secreted zymogen and operates outside the cell. Therefore, its functional venue is the GO:0005576 extracellular region, where zymogen activation, inhibitor sequestration, and substrate presentation occur.\n\nMechanistically, I hypothesize a secreted zymogen that is activated by limited proteolysis to expose the catalytic machinery defined by the histidine (69–74) and serine (210–221) motifs. Once active, it binds and cleaves extracellular targets via elastase-like specificity, thereby tuning insulin-related pathways and platelet responses. Likely interaction partners include endogenous serine protease inhibitors (serpins and Kunitz-type inhibitors) that regulate activity, extracellular matrix and adhesion components that present substrates, and hormone-processing assemblies that coordinate insulin handling. This ensemble of interactions positions the protease as an extracellular modulator of proteolysis with downstream effects on endocrine and hemostatic systems.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P08218.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P08218"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P08218/entry","atlas":"/p/P08218"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}