{"uniprot":"P0C7U1","gene":"ASAH2B","name":"Putative inactive neutral ceramidase B","organism":"Homo sapiens (Human)","status":"dark","length":165,"sequence":"MRQHRQFMDRTHYLLTFSSSETLLRLLLRIVDRAPKGRTFGDVLQPAKPEYRVGEVAEVIFVGANPKNSVQNQTHQTFLTVEKYEATSTSWQIVCNDASWETRFYWHKGLLGLSNATVEWHIPDTAQPGIYRIRYFGHNRKQDILKPAVILSFEGTSPAFEVVTI","function_summary":"A soluble human enzyme that hydrolyzes ceramide at neutral to alkaline pH to generate sphingosine and free fatty acids, thereby tuning sphingolipid signaling pathways that govern apoptosis and differentiation. A substantial cytosolic pool performs neutral ceramidase chemistry, while a nucleoplasmic fraction associates with chromatin and spliceosomal assemblies to modulate pre-mRNA splicing. Its mechanism centers on a conserved ceramidase catalytic core supported by protein-binding interfaces that enable oligomerization and assembly with RNA-processing machinery, coupling metabolic cues to nuclear RNA processing.","plain_language":"ASAH2B has barely been studied. The model's best guess: A soluble human enzyme that hydrolyzes ceramide at neutral to alkaline pH to generate sphingosine and free fatty acids, thereby tuning sphingolipid signaling pathways that govern apoptosis and differentiation. A substantial cytosolic pool performs neutral ceramidase chemistry, while a nucleoplasmic fraction associates with chromatin and spliceosomal assemblies to modulate pre-mRNA splicing.","uniprot_summary":"Hydrolyzes the sphingolipid ceramide into sphingosine and free fatty acid.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0000398","label":"mRNA splicing, via spliceosome"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"},{"id":"GO:0005654","label":"nucleoplasm"}]},"interpro":[{"id":"IPR038445","name":"Neutral ceramidase, C-terminal domain superfamily","type":"homologous_superfamily","start":29,"end":165},{"id":"IPR031331","name":"Neutral/alkaline non-lysosomal ceramidase, C-terminal","type":"domain","start":29,"end":162},{"id":"IPR006823","name":"Neutral/alkaline nonlysosomal ceramidase","type":"family","start":26,"end":163}],"reasoning":"I begin with the InterPro architecture. Three concordant signatures define a neutral/alkaline non-lysosomal ceramidase core that occupies the C-terminal two-thirds of the protein: IPR006823 (Neutral/alkaline nonlysosomal ceramidase, family) spans residues 26–163; within it, IPR031331 (Neutral/alkaline non-lysosomal ceramidase, C-terminal domain) extends from residues 29–162; and this is encompassed by IPR038445 (Neutral ceramidase, C-terminal domain superfamily) from residues 29–165. The tight clustering of ceramidase-family and C-terminal-domain signatures indicates a conserved catalytic scaffold that hydrolyzes the amide bond of N-acylsphingosines at neutral to alkaline pH. The absence of additional catalytic modules and the dominance of a single enzymatic core argue that the primary molecular function is hydrolysis of ceramides to sphingosine and fatty acids. Such enzymes often rely on oligomerization and adaptor contacts, which rationalizes a capacity for protein binding (GO:0005515) as an auxiliary function that stabilizes complexes and targets the enzyme to specific cellular locales.\n\nFrom this enzymatic foundation, I infer the biological role. Ceramide turnover directly feeds into sphingolipid signaling pathways that govern apoptosis, differentiation, and stress responses. The explicit catalytic architecture that produces sphingosine positions the protein as a regulator of sphingolipid flux rather than a bulk catabolic enzyme. A second axis of evidence arises from cellular localization and nuclear coupling: the protein is detected in the cytosol and nucleoplasm and associates with chromatin. This spatial coupling provides a mechanistic route to influence pre-mRNA processing. Specifically, the nucleoplasmic pool can physically engage spliceosomal assemblies and RNA-processing hubs, aligning with mRNA splicing via the spliceosome (GO:0000398). Thus, the ceramidase architecture supplies the metabolic input, while nucleoplasmic residency and protein-binding capacity provide the conduit to modulate splicing.\n\nCellular location follows directly from the dual architecture and binding behavior. The ceramidase core lacks transmembrane segments and secretion signals, favoring a soluble intracellular enzyme. Its soluble pool is partitioned between the cytosol (GO:0005829) and nucleoplasm (GO:0005654), consistent with a model in which cytosolic ceramide hydrolysis is coordinated with nuclear events. Chromatin association further refines the nucleoplasmic localization and suggests transient residence at transcription-splicing interfaces.\n\nThese lines of evidence converge on a mechanistic hypothesis. The ceramidase domain hydrolyzes ceramide in the cytosol, tuning the local balance of sphingolipids that signal to apoptosis and differentiation pathways. A fraction of the enzyme traffics to the nucleoplasm, where its protein-binding surfaces assemble with spliceosomal factors and chromatin-bound RNA-processing machinery. Through this, it couples metabolic state to pre-mRNA splicing decisions. Likely interaction partners include spliceosome components (e.g., U2AF and SF3 complexes), serine/arginine-rich splicing regulators, and chromatin-associated adaptors that tether the enzyme to RNA-processing sites. This dual localization and binding propensity explain both enzymatic sphingolipid control and a modulatory role in nuclear RNA splicing.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P0C7U1.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P0C7U1"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P0C7U1/entry","atlas":"/p/P0C7U1"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}