Histidinol-phosphate aminotransferase (HisC; EC 2.6.1.9), a cytoplasmic pyridoxal-5'-phosphate (PLP)-dependent class-II aminotransferase that catalyzes the seventh step of L-histidine biosynthesis. It transfers an amino group from L-glutamate to imidazole-acetol phosphate (3-(imidazol-4-yl)-2-oxopropyl phosphate), producing L-histidinol phosphate and 2-oxoglutarate. The enzyme functions as a homodimer with active sites at the dimer interface; PLP is covalently bound as an internal aldimine to an active-site lysine (Lys210 in this protein) and catalysis proceeds via a ping-pong mechanism through a pyridoxamine-5'-phosphate intermediate. In Pseudomonas putida KT2440 the gene (PP_0967) lies within a histidine-biosynthesis gene cluster. Aromatic-amino-acid transamination is documented for some HisC orthologs but has not been demonstrated for the KT2440 protein.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000105 L-histidine biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: HisC catalyzes the seventh step of histidine biosynthesis; this BP term is well supported by family/HAMAP-rule assignment, the UniProt pathway annotation, and operon context in KT2440. Reason: Core biological process for this enzyme. The histidinol-phosphate aminotransferase function places it squarely in the L-histidine biosynthetic pathway (UniPathway UPA00031; HAMAP-Rule MF_01023). Supporting Evidence: file:PSEPK/hisC/hisC-deep-research-openscientist.md catalyzes the **seventh step of de novo L-histidine biosynthesis** |
| GO:0004400 L-histidinol-phosphate:2-oxoglutarate transaminase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the specific molecular function of HisC (EC 2.6.1.9), transaminating L-histidinol phosphate with 2-oxoglutarate/L-glutamate. The UniProt CATALYTIC ACTIVITY block and HAMAP rule directly support this. Reason: Represents the core molecular function. Strongly supported by family assignment (HisP_aminotrans subfamily, TIGR01141 hisC), Rhea:23744, and EC 2.6.1.9. Supporting Evidence: file:PSEPK/hisC/hisC-deep-research-openscientist.md *hisC* encodes **histidinol-phosphate aminotransferase (HisC, EC 2.6.1.9)** |
| GO:0016740 transferase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: A high-level parent of the specific aminotransferase activity already annotated (GO:0004400). It is correct but uninformative given the more precise term. Reason: Redundant generic ancestor of GO:0004400; adds no information beyond the specific transaminase MF term. |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: HisC is a PLP-dependent enzyme that covalently binds pyridoxal 5'-phosphate as an internal aldimine at the active-site lysine (MOD_RES 210 in this entry). Well supported by the COFACTOR annotation and conserved PLP-lysine motif. Reason: PLP binding is an essential, well-supported cofactor interaction, but the substrate-specific transaminase activity is the defining molecular function. The PLP-lysine internal aldimine and ping-pong mechanism are documented for HisC homologs (see hisC-deep-research-falcon.md). |
| GO:0140385 amino acid transaminase activity | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: A broad parent term covering aminotransferase activity on amino acid substrates. Correct but less specific than GO:0004400, which is already annotated. Reason: Generic ancestor of the specific histidinol-phosphate transaminase activity; the more precise term GO:0004400 already captures this function. |
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