{"uniprot":"A6NFU8","gene":"PGPEP1L","name":"Pyroglutamyl-peptidase 1-like protein","organism":"Homo sapiens (Human)","status":"dark","length":196,"sequence":"MKPRTLVELSKLGLGNETVVQLRTLELPVDYREAKRRVTGIWEDHQPQLVVHVGMDTAAKAIILEQSGKNQGYRDADIRSFWPEGGVCLPGSPDVLESGVCMKAVCKRVAVEGVDVIFSRDAGRYVCDYTYYLSLHHGKGCAALIHVPPLSRGLPASLLGRALRVIIQEMLEEVGKPKHRAQFEENSTMVLPAKGN","function_summary":"A soluble cytosolic metalloprotease that removes N-terminal pyroglutamate from intracellular peptides, thereby unblocking their N-termini and feeding them back into general peptide turnover. By catalyzing this key terminal step in peptide maturation and clearance, it sustains intracellular proteolysis and amino acid economy within the cytoplasm. Its soluble architecture and transient macromolecular contacts position it as a central node in cytosolic peptide-processing pathways.","plain_language":"PGPEP1L has barely been studied. The model's best guess: A soluble cytosolic metalloprotease that removes N-terminal pyroglutamate from intracellular peptides, thereby unblocking their N-termini and feeding them back into general peptide turnover. By catalyzing this key terminal step in peptide maturation and clearance, it sustains intracellular proteolysis and amino acid economy within the cytoplasm.","uniprot_summary":"Pyroglutamyl-peptidase I.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0006508","label":"proteolysis"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"}]},"interpro":[{"id":"IPR036440","name":"Peptidase C15, pyroglutamyl peptidase I-like superfamily","type":"homologous_superfamily","start":4,"end":184},{"id":"IPR016125","name":"Peptidase C15, pyroglutamyl peptidase I-like","type":"family","start":8,"end":172}],"reasoning":"I begin with the InterPro architecture. The sequence is dominated by IPR036440 (Peptidase C15, pyroglutamyl peptidase I-like superfamily, residues 4–184), within which sits IPR016125 (Peptidase C15, pyroglutamyl peptidase I-like family, residues 8–172). This nested arrangement—an explicit C15 peptidase family core embedded in its broader superfamily—defines a cytosolic C15 metalloprotease fold specialized for removing N-terminal pyroglutamate (5-oxoproline) from peptides. The C15 architecture dictates a metalloprotease active site that hydrolyzes the peptide bond immediately after a blocked N-terminus, thereby unmasking a free amino group and terminating the inhibitory pyroglutamyl cap.\n\nThis domain architecture causally specifies molecular function. The C15 peptidase scaffold creates a catalytic pocket that accommodates N-terminally blocked substrates and catalyzes hydrolysis; this is the biochemical essence of proteolysis. Such enzymes often rely on transient macromolecular contacts to position substrates and assemble with cellular partners, which supports GO:0005515 protein binding as an auxiliary function. The catalytic role directly drives GO:0006508 proteolysis by converting otherwise refractory pyroglutamylated peptides into processable intermediates.\n\nFrom function to process, removal of N-terminal pyroglutamate is a decisive step in peptide turnover and maturation pathways. By stripping the pyroglutamyl cap, the enzyme feeds peptides back into general proteolytic routes, coupling cytosolic peptide clearance to broader amino acid and peptide homeostasis. This mechanistic coupling explains its central role in intracellular peptide processing.\n\nCellular location follows from both the soluble C15 fold and the absence of transmembrane or secretion signals. The enzyme operates as a soluble protease in the cytoplasm, with its steady-state pool concentrated in the aqueous phase of the cytoplasm. This supports localization to the cytoplasm and more specifically the GO:0005829 cytosol, consistent with a soluble metalloprotease that surveys cytosolic peptide pools.\n\nMechanistically, the enzyme likely recognizes the pyroglutamyl ring via a stereoselective binding groove and uses a metal-activated water molecule for nucleophilic attack at the peptide’s N-terminal bond. Substrate selection is enforced by a pocket that tolerates the cyclic pG cap and adjacent residues, ensuring efficient trimming of blocked peptides. In this cytosolic context, plausible interaction partners include peptide-generating systems and downstream peptidases that hand off substrates after cap removal. I hypothesize transient assemblies with cytosolic peptidyl-dipeptidases and amino acid–producing enzymes to channel products efficiently and prevent accumulation of refractory pyroglutamylated intermediates.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-A6NFU8.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/A6NFU8"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/A6NFU8/entry","atlas":"/p/A6NFU8"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}