{"entryType":"UniProtKB reviewed (Swiss-Prot)","primaryAccession":"Q8R207","secondaryAccessions":["Q8BHT2"],"uniProtkbId":"SPTSA_MOUSE","entryAudit":{"firstPublicDate":"2005-07-05","lastAnnotationUpdateDate":"2026-09-02","lastSequenceUpdateDate":"2009-05-26","entryVersion":132,"sequenceVersion":2},"annotationScore":4.0,"organism":{"scientificName":"Mus musculus","commonName":"Mouse","taxonId":10090,"lineage":["Eukaryota","Metazoa","Chordata","Craniata","Vertebrata","Euteleostomi","Mammalia","Eutheria","Euarchontoglires","Glires","Rodentia","Myomorpha","Muroidea","Muridae","Murinae","Mus","Mus"]},"proteinExistence":"3: Inferred from homology","proteinDescription":{"recommendedName":{"fullName":{"evidences":[{"evidenceCode":"ECO:0000305"}],"value":"Serine palmitoyltransferase small subunit A"}},"alternativeNames":[{"fullName":{"value":"Small subunit of serine palmitoyltransferase A"},"shortNames":[{"value":"ssSPTa"}]}]},"genes":[{"geneName":{"evidences":[{"evidenceCode":"ECO:0000312","source":"MGI","id":"MGI:1913399"}],"value":"Sptssa"},"synonyms":[{"value":"Ssspta"}]}],"comments":[{"texts":[{"evidences":[{"evidenceCode":"ECO:0000250","source":"UniProtKB","id":"Q969W0"}],"value":"Component of the serine palmitoyltransferase multisubunit enzyme (SPT) that catalyzes the initial and rate-limiting step in sphingolipid biosynthesis by condensing L-serine and activated acyl-CoA (most commonly palmitoyl-CoA) to form long-chain bases. The SPT complex is composed of SPTLC1, SPTLC2 or SPTLC3 and SPTSSA or SPTSSB. Within this complex, the heterodimer consisting of SPTLC1 and SPTLC2/SPTLC3 forms the catalytic core. Within the SPT complex, SPTSSA stimulates the catalytic activity and plays a role in substrate specificity, which depends upon the overall complex composition. The SPTLC1-SPTLC2-SPTSSA complex shows a strong preference for C16-CoA substrate, while the SPTLC1-SPTLC3-SPTSSA isozyme uses both C14-CoA and C16-CoA as substrates, with a slight preference for C14-CoA. Independently of its action as a SPT component, may be involved in MBOAT7 localization to mitochondria-associated membranes, a membrane bridge between the endoplasmic reticulum and mitochondria, may hence affect MBOAT7-catalyzed incorporation of arachidonic acid into phosphatidylinositol"}],"commentType":"FUNCTION"},{"texts":[{"value":"Lipid metabolism; sphingolipid metabolism"}],"commentType":"PATHWAY"},{"texts":[{"evidences":[{"evidenceCode":"ECO:0000250","source":"UniProtKB","id":"Q969W0"}],"value":"Component of the serine palmitoyltransferase (SPT) complex, which is composed of SPTLC1, SPTLC2 or SPTLC3 and SPTSSA or SPTSSB. The heterodimer consisting of SPTLC1 and SPTLC2/SPTLC3 forms the catalytic core of the enzyme, while SPTSSA or SPTSSB subunits determine substrate specificity. SPT also interacts with ORMDL proteins, especially ORMDL3, which negatively regulate SPT activity in the presence of ceramides. Interacts with MBOAT7; the interaction plays a role in MBOAT7 localization to mitochondria-associated membranes"}],"commentType":"SUBUNIT"},{"commentType":"SUBCELLULAR LOCATION","subcellularLocations":[{"location":{"evidences":[{"evidenceCode":"ECO:0000305"}],"value":"Endoplasmic reticulum membrane","id":"SL-0097"},"topology":{"evidences":[{"evidenceCode":"ECO:0000305"}],"value":"Multi-pass membrane protein","id":"SL-9909"}}]},{"texts":[{"evidences":[{"evidenceCode":"ECO:0000305"}],"value":"Belongs to the SPTSS family. 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