{"uniprot":"Q7Z5L3","gene":"C1QL2","name":"Complement C1q-like protein 2","organism":"Homo sapiens (Human)","status":"dark","length":287,"sequence":"MALGLLIAVPLLLQAAPRGAAHYEMMGTCRMICDPYTAAPGGEPPGAKAQPPGPSTAALEVMQDLSANPPPPFIQGPKGDPGRPGKPGPRGPPGEPGPPGPRGPPGEKGDSGRPGLPGLQLTAGTASGVGVVGGGAGVGGDSEGEVTSALSATFSGPKIAFYVGLKSPHEGYEVLKFDDVVTNLGNHYDPTTGKFSCQVRGIYFFTYHILMRGGDGTSMWADLCKNGQVRASAIAQDADQNYDYASNSVVLHLDSGDEVYVKLDGGKAHGGNNNKYSTFSGFLLYPD","function_summary":"A secreted extracellular organizer that assembles into multimeric complexes to scaffold synapse formation and maturation. Its collagen-like stalk and globular head create a high-avidity platform that binds synaptic receptors and adhesion molecules, driving synaptogenesis and broader neural circuit development in brain and retina. By clustering ion channels and neurotransmitter receptors at nascent synapses, it coordinates innervation, neuronal and glial maturation, and specialized pathways underlying eye development.","plain_language":"C1QL2 has barely been studied. The model's best guess: A secreted extracellular organizer that assembles into multimeric complexes to scaffold synapse formation and maturation. Its collagen-like stalk and globular head create a high-avidity platform that binds synaptic receptors and adhesion molecules, driving synaptogenesis and broader neural circuit development in brain and retina.","uniprot_summary":"Involved in synaptogenesis and neuronal circuit development and maturation in the brain.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0060384","label":"innervation"},{"id":"GO:0042551","label":"neuron maturation"},{"id":"GO:0007423","label":"sensory organ development"},{"id":"GO:0007416","label":"synapse assembly"},{"id":"GO:0050767","label":"regulation of neurogenesis"},{"id":"GO:0045161","label":"neuronal ion channel clustering"},{"id":"GO:0048666","label":"neuron development"},{"id":"GO:0043010","label":"camera-type eye development"},{"id":"GO:0014013","label":"regulation of gliogenesis"}],"cellular_component":[{"id":"GO:0032991","label":"protein-containing complex"},{"id":"GO:0005576","label":"extracellular region"},{"id":"GO:0031012","label":"extracellular matrix"},{"id":"GO:0062023","label":"collagen-containing extracellular matrix"}]},"interpro":[{"id":"IPR008983","name":"Tumour necrosis factor-like domain superfamily","type":"homologous_superfamily","start":152,"end":287},{"id":"IPR001073","name":"C1q domain","type":"domain","start":152,"end":287},{"id":"IPR050822","name":"Cerebellin Synaptic Organizer","type":"family","start":27,"end":287},{"id":"IPR008160","name":"Collagen triple helix repeat","type":"repeat","start":76,"end":120}],"reasoning":"I begin with the InterPro architecture. The N-terminal third is encompassed by IPR050822 (Cerebellin Synaptic Organizer family, residues 27–287), which frames the entire polypeptide as a secreted synaptic organizer. Within this scaffold, residues 76–120 carry IPR008160 (Collagen triple helix repeat), a hallmark of secreted, trimer-forming assemblies that stabilize higher-order extracellular structures. The C-terminal half (residues 152–287) contains IPR001073 (C1q domain) and is simultaneously classified in IPR008983 (Tumour necrosis factor-like domain superfamily), indicating a globular C1q/TNF-like β-sandwich that typically trimerizes and mediates avid extracellular binding. The ordered layout—an N-terminal collagen-like stalk feeding into a C-terminal C1q/TNF-like head—is a canonical secreted organizer architecture that causes multivalent protein binding and extracellular matrix association.\n\nThis domain architecture dictates molecular function. The collagen-like repeat and the C1q/TNF-like head together create a multimeric platform optimized for avid, modular interactions rather than catalysis. Such assemblies operate by docking to other proteins and extracellular matrix components, which directly supports GO:0005515 protein binding as the primary molecular function.\n\nFrom this binding-centric chemistry, the biological processes follow. A cerebellin-family organizer (IPR050822) is specialized for building synaptic architecture. By assembling trimers that bridge extracellular and membrane-associated partners, it drives GO:0007416 synapse assembly. The same organizing principle—multivalent extracellular scaffolding that nucleates presynaptic and postsynaptic specializations—extends to tissue-level wiring, aligning with GO:0060384 innervation and GO:0050767 regulation of neurogenesis. The capacity to cluster membrane proteins emerges naturally from this scaffold: the C1q/TNF-like head can tether to receptor/adhesion complexes, producing GO:0045161 neuronal ion channel clustering. In specialized circuits of the retina and cerebellum, this organizer function scales to developmental programs captured by GO:0042551 neuron maturation and GO:0043010 camera-type eye development. Its influence on glial maturation pathways, often coordinated through synaptic cues and extracellular signaling, accounts for GO:0014013 regulation of gliogenesis.\n\nCellular location is dictated by secretion and matrix affinity. The collagen-like repeat and C1q/TNF-like head target the extracellular milieu, consistent with a secreted protein that assembles into higher-order oligomers. This places the protein in GO:0005576 extracellular region and GO:0062023 collagen-containing extracellular matrix. Its propensity to form multimeric assemblies and to function as an extracellular bridge aligns with GO:0032991 protein-containing complex.\n\nMechanistically, I hypothesize that the protein is secreted as a trimeric unit via its collagen-like stalk, presenting a C1q/TNF-like head that binds synaptic receptors and adhesion molecules. This multivalency clusters ion channels and neurotransmitter receptors at developing synapses, thereby stabilizing synaptic contacts and guiding circuit maturation. Likely interaction partners include presynaptic neurexins and postsynaptic neuroligins that form trans-synaptic bridges, as well as ion channel complexes and adhesion modules that require extracellular organizers to achieve stable clustering. Through these assemblies, the protein orchestrates synaptogenesis and broader neural circuit development in brain and retina.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q7Z5L3.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q7Z5L3"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q7Z5L3/entry","atlas":"/p/Q7Z5L3"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}