{"uniprot":"Q8N7X8","gene":"SIGLECL1","name":"SIGLEC family-like protein 1","organism":"Homo sapiens (Human)","status":"dark","length":197,"sequence":"MLPLLQLVPAKLLNSSCSLEKTLQCSCSFHGIPTPSVQWWMGGVPVGVDGMDGSLQVTSTMLGPWANSTISLTEEPEMGMRLLCEGKNQNGTHALSILLMSRKSSLAAQAFVKGLIQGAIYAGIVIALLFLCLLPLIVKHIRKKQAKKAAAIRAKKSSKVRASQELEMSLKPEEPGKPVVATFSESRILEKQDKRAS","function_summary":"A single-pass cell-surface lectin that presents a two-Ig ectodomain to recognize sialylated glycans and assemble binding platforms at the plasma membrane. By clustering with membrane partners and recruiting cytoplasmic trafficking machinery, it modulates adhesion and signaling pathways that influence neural development and immune tuning. It resides at the cell surface and can be stored on platelet alpha granule membranes, positioning it to regulate glycan-guided interactions and endocytic routing that impact substantia nigra neuron development.","plain_language":"SIGLECL1 has barely been studied. The model's best guess: A single-pass cell-surface lectin that presents a two-Ig ectodomain to recognize sialylated glycans and assemble binding platforms at the plasma membrane. By clustering with membrane partners and recruiting cytoplasmic trafficking machinery, it modulates adhesion and signaling pathways that influence neural development and immune tuning.","uniprot_summary":"Putative sialic acid-binding immunoglobulin-like lectin.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0021762","label":"substantia nigra development"}],"cellular_component":[{"id":"GO:0005886","label":"plasma membrane"},{"id":"GO:0031091","label":"platelet alpha granule membrane"}]},"interpro":[{"id":"IPR013783","name":"Immunoglobulin-like fold","type":"homologous_superfamily","start":10,"end":109},{"id":"IPR036179","name":"Immunoglobulin-like domain superfamily","type":"homologous_superfamily","start":18,"end":106},{"id":"IPR061941","name":"Sialic acid binding Ig-like lectin, C-terminal domain","type":"domain","start":101,"end":161},{"id":"IPR051036","name":"Sialic acid-binding Ig-like lectin","type":"family","start":14,"end":164}],"reasoning":"I begin with the InterPro architecture. The N-terminal half contains IPR013783 (Immunoglobulin-like fold, residues 10–109) and the overlapping IPR036179 (Immunoglobulin-like domain superfamily, residues 18–106), establishing a classical Ig-like β-sandwich scaffold that forms a rigid extracellular binding module. Immediately downstream lies IPR061941 (Sialic acid binding Ig-like lectin, C-terminal domain, residues 101–161), which completes the two-Ig-domain ectodomain typical of Siglec-type receptors. The entire extracellular region is encompassed by IPR051036 (Sialic acid-binding Ig-like lectin family, residues 14–164), specifying membership in the Siglec family. This ordered layout—an N-terminal Ig-like domain followed by a Siglec-specific C-terminal Ig-like domain—creates a composite lectin surface that recognizes terminal sialylated glycans. The absence of intracellular catalytic motifs and the presence of a single-pass type I topology indicate that signaling is mediated by extracellular ligand binding and cytoplasmic tail motifs rather than enzymatic chemistry.\n\nThis Ig lectin architecture causes a molecular function centered on avid protein and glycan-mediated interactions. The β-sandwich domains provide a stable platform for high-specificity binding to sialylated glycoconjugates and to protein partners in cis or trans. This supports GO:0005515 protein binding as the operative molecular function, with binding specificity tuned by the Siglec ectodomain.\n\nFrom this binding capacity, I infer roles in neural development and immune modulation. Siglec-type receptors on neural cells can interpret sialylation landscapes that change during brain maturation. Such glycan-guided adhesion and signaling plausibly contribute to patterning and survival pathways that culminate in region-specific neurodevelopment, aligning with GO:0021762 substantia nigra development. In immune contexts, the same lectin surface can dampen or tune activation thresholds by clustering with membrane partners and endocytic machinery.\n\nThe cellular component follows directly from the topology. A signal peptide and luminal Ig-like ectodomain precede a single transmembrane helix and short cytoplasmic tail, placing the receptor at the cell surface as a single-pass type I membrane protein. This situates the protein at the GO:0005886 plasma membrane. The presence of the same architecture in secretory lineages and its documented storage in hematopoietic compartments explains localization to GO:0031091 platelet alpha granule membrane, where the receptor can be stockpiled and mobilized during platelet activation.\n\nMechanistically, the ectodomain binds sialylated glycans on neighboring cells or within the same membrane, driving receptor clustering. Clustering recruits cytoplasmic adaptors and endocytic machinery through short intracellular motifs, enabling internalization and signaling attenuation. I hypothesize that the receptor transiently associates with integrins and other adhesion receptors to modulate cell–cell contacts and with endocytic adaptors to traffic bound complexes. In platelets and immune cells, this coupling would fine-tune activation and developmental signaling pathways that intersect with substantia nigra neuron maturation and maintenance.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q8N7X8.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q8N7X8"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q8N7X8/entry","atlas":"/p/Q8N7X8"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}