tyrB (PP_1972; also referred to as tyrB-1) is a cytoplasmic, pyridoxal 5'-phosphate (PLP)-dependent aminotransferase of the class-I (fold-type I) aspartate aminotransferase superfamily. It catalyzes reversible transamination in which an amino group is transferred from an amino acid donor to a 2-oxoacid acceptor (commonly 2-oxoglutarate, yielding L-glutamate). It is annotated as an aromatic-amino-acid aminotransferase, interconverting aromatic amino acids (L-tyrosine, L-phenylalanine) and their cognate aromatic 2-oxoacids (4-hydroxyphenylpyruvate, phenylpyruvate), and contributes to aromatic amino acid biosynthesis and catabolism. Like many class-I PLP aminotransferases it is a homodimer with active sites formed at the subunit interface. In P. putida KT2440 it is one of several aminotransferase isozymes acting on aromatic amino acids; genetic studies show that loss of tyrB alone causes only mild aromatic-amino-acid utilization phenotypes because of redundancy with paralogous aminotransferases (notably PP_3590/AmaC and tyrB-2/phhC), so its physiological role overlaps with those enzymes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic root-level molecular function term. tyrB is an enzyme, so this is not wrong, but it is uninformatively general and is fully subsumed by the more specific transaminase/aminotransferase activity terms. Reason: "catalytic activity" is the MF root and conveys no specific information. The more precise terms GO:0008483 (transaminase activity) and GO:0004838 (L-tyrosine:2-oxoglutarate transaminase activity) capture the actual function. |
| GO:0004838 L-tyrosine:2-oxoglutarate transaminase activity | IEA GO_REF:0000118 | ACCEPT | Summary: Specific aromatic (tyrosine) aminotransferase activity assigned by TreeGrafter from the PTHR11879:SF37 "aromatic-amino-acid aminotransferase" subfamily. This is consistent with the protein family, the COG1448 assignment, and with biochemical/genetic characterization of P. putida aromatic aminotransferases. This is the best representation of the gene's core molecular function. Reason: Domain/family evidence (class-I PLP aminotransferase, PANTHER ArAT subfamily SF37) plus genetic evidence in KT2440 (tyrB mutants show a tyrosine-utilization phenotype; PMID:20050871) support tyrosine aminotransferase activity. The enzyme is likely promiscuous across aromatic amino acids (also acting on phenylalanine), but this term well captures the central characterized activity. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: Cytosolic localization predicted by TreeGrafter. Soluble class-I PLP aminotransferases acting in amino acid metabolism are cytoplasmic enzymes; the sequence has no signal peptide or transmembrane region. Consistent with the expected localization. Reason: Aromatic aminotransferases in this family are soluble cytoplasmic enzymes. No experimental KT2440 localization data exist, but the prediction is biologically appropriate and there is no evidence for periplasmic/membrane localization. |
| GO:0006520 amino acid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Broad biological process term. tyrB participates in (aromatic) amino acid metabolism, so this is correct but general. A more specific process such as aromatic amino acid family metabolism / phenylalanine or tyrosine biosynthesis or catabolism would be more informative. Reason: The annotation is correct in essence but too high-level. tyrB acts specifically on aromatic amino acids (Tyr/Phe), so the more specific "aromatic amino acid family metabolic process" better reflects the characterized role while remaining defensible from family + genetic evidence. (Chorismate metabolic process is not appropriate: tyrB acts downstream of chorismate on the aromatic amino acids/2-oxoacids, not on chorismate itself.) Proposed replacements: aromatic amino acid family metabolic process |
| GO:0008483 transaminase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: General transaminase (aminotransferase) activity. Correct and well supported by the class-I PLP-dependent aminotransferase family assignment, but less specific than GO:0004838. Useful as a parent term. Reason: Accurately describes the enzymatic class but is a parent of the more specific aromatic aminotransferase term that represents the core function. Retain as supporting/non-core rather than as the primary MF. |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000120 | ACCEPT | Summary: PLP cofactor binding. tyrB is a PLP-dependent enzyme (UniProt COFACTOR: pyridoxal 5'-phosphate; conserved PROSITE PS00105 class-I aminotransferase PLP-binding motif). This is a well-supported and informative molecular function annotation. Reason: Strong family/motif evidence (IPR004838/IPR004839, PROSITE AA_TRANSFER_ CLASS_1, UniProt cofactor annotation) for PLP binding, which is essential for the transamination mechanism. |
| GO:0042802 identical protein binding | IEA GO_REF:0000118 | MARK AS OVER ANNOTATED | Summary: Self-association annotation reflecting the homodimeric quaternary structure typical of class-I aminotransferases (UniProt SUBUNIT: Homodimer). While the homodimer assignment is reasonable, "identical protein binding" is an uninformative interaction term that does not convey biological function and is a frequent TreeGrafter over-propagation. Reason: Homodimerization is a structural property rather than a distinct molecular function; the term adds little and is propagated electronically without direct evidence for this protein. Per curation guidance, generic "protein binding"-type terms are discouraged. |
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Download this section (compressed HTML)Q: What is the in vitro substrate range and kinetic preference of purified PP_1972 (Tyr vs Phe vs Trp; 2-oxoglutarate vs pyruvate as acceptor), given that direct enzymology exists for the paralogs but not for PP_1972 itself?
Q: What is the division of labor among the P. putida KT2440 aromatic aminotransferase isozymes (PP_1972/tyrB-1, PP_3590/AmaC, tyrB-2/phhC) in aromatic amino acid biosynthesis versus catabolism, and under what conditions is PP_1972 non-redundant?
Experiment: Express and purify recombinant PP_1972 and determine kinetic constants (Km/kcat) against a panel of amino donors (Tyr, Phe, Trp, Asp) and 2-oxoacid acceptors to define substrate specificity directly.
Experiment: Construct single and combinatorial in-frame deletions of PP_1972, PP_3590, and tyrB-2/phhC and assay growth on aromatic amino acids as sole nitrogen and carbon sources to resolve the redundancy network and any condition-specific, non-redundant role of PP_1972.
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