thrB (PA5495) encodes homoserine kinase (EC 2.7.1.39) of Pseudomonas aeruginosa, a type II homoserine kinase of the aminoglycoside phosphotransferase (protein-kinase-like) fold that is unrelated to the GHMP-family homoserine kinases of Escherichia coli and Bacillus subtilis. It phosphorylates L-homoserine with ATP to give O-phospho-L-homoserine, the fourth of five steps of L-threonine synthesis from aspartate, between homoserine dehydrogenase (Hom) and threonine synthase (ThrC). Unlike the other thr genes, thrB lies apart from the hom-thrC operon. Its loss alone does not cause threonine auxotrophy because ThrH, a phosphoserine phosphatase with phosphoserine:homoserine phosphotransferase activity, provides a parallel route to O-phospho-L-homoserine; only thrB thrH double mutants require threonine. Its activity is inferred from family membership and genetics; the purified PA5495 enzyme has not been characterised.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004413 homoserine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001464661 (10 leaf IBAs), whose homoserine kinase IBD has a single seed, this gene's PseudoCAP IDA row. The target appearing in its own WITH/FROM is expected, not circular. Reason: For PA5495 itself the activity is well supported by family evidence (HAMAP MF_00301 type II HSK) and genetics: thrB and thrH are redundant for threonine synthesis, and ThrH reaches phosphohomoserine by a different, ATP-independent chemistry, so ThrB is the ATP-dependent kinase. The seed's assay is not visible (see the IDA row), and the node also covers B. subtilis AmiN, an amicoumacin kinase; that concerns another leaf and is flagged. Supporting Evidence: file:PSEAE/thrB/thrB-uniprot.txt Belongs to the pseudomonas-type ThrB family. PMID:10220164 In P. aeruginosa, threonine auxotrophy is observed only when both thrB and thrH are simultaneously inactivated. |
| GO:0004413 homoserine kinase activity | IDA PMID:10220164 ThrH, a homoserine kinase isozyme with in vivo phosphoserine... | ACCEPT | Summary: PseudoCAP IDA; sole seed of the PTN001464661 homoserine kinase IBD and one of two seeds of the PTN001464650 amino acid kinase IBD. Patte et al. 1999 is a genetic study of thrB and the isozyme thrH. Reason: Right gene and, unlike the same PMID on hom, the right paper: it is about thrB. The activity is correct for PA5495 on family and genetic grounds. But the abstract describes no direct assay of ThrB; its evidence is the threonine auxotrophy of the thrB thrH double mutant, which supports the process rather than this specific activity. The full text could not be read, so I defer to the curator on the claim and flag the evidence code. Supporting Evidence: PMID:10220164 Homoserine kinase, the product of the thrB gene, catalyses an obligatory step of threonine biosynthesis. file:PSEAE/thrB/thrB-uniprot.txt Belongs to the pseudomonas-type ThrB family. |
| GO:0004413 homoserine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HAMAP MF_00301 / InterPro / EC / Rhea-based homoserine kinase activity. Reason: Same correct core claim, from the curated type II HSK family rule. Supporting Evidence: file:PSEAE/thrB/thrB-uniprot.txt Reaction=L-homoserine + ATP = O-phospho-L-homoserine + ADP + H(+); |
| GO:0009088 L-threonine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001464661; sole seed is this gene's PseudoCAP IDA row for L-threonine biosynthetic process. Reason: ThrB catalyses step 4 of threonine synthesis, and the double-mutant auxotrophy shows that it contributes to the pathway in vivo. Correct for this gene; the node-breadth concern is recorded on the MF IBA row. Supporting Evidence: PMID:10220164 In P. aeruginosa, threonine auxotrophy is observed only when both thrB and thrH are simultaneously inactivated. file:PSEAE/thrB/thrB-uniprot.txt L-threonine biosynthesis; L-threonine from L-aspartate: step 4/5. |
| GO:0009088 L-threonine biosynthetic process | IDA PMID:10220164 ThrH, a homoserine kinase isozyme with in vivo phosphoserine... | ACCEPT | Summary: PseudoCAP IDA; sole seed of the PTN001464661 L-threonine biosynthetic process IBD. Reason: Sound claim on the right paper: threonine auxotrophy appears only when thrB and thrH are both inactivated, so thrB contributes to threonine synthesis, and its product catalyses a step of the pathway. The evidence the abstract reports is a genetic interaction, so IGI (with thrH, PA1757) probably fits better than IDA; the full text was not read. Supporting Evidence: PMID:10220164 In P. aeruginosa, threonine auxotrophy is observed only when both thrB and thrH are simultaneously inactivated. |
| GO:0009088 L-threonine biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: HAMAP/UniPathway-based L-threonine biosynthetic process. Reason: Same correct process claim as the IBA and IDA rows. Supporting Evidence: file:PSEAE/thrB/thrB-uniprot.txt L-threonine biosynthesis; L-threonine from L-aspartate: step 4/5. |
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Download this section (compressed HTML)Q: Does the full text of Patte et al. 1999 (PMID:10220164) contain a homoserine kinase assay of ThrB (purified, or extracts of thrB versus thrH mutants)? If not, the PseudoCAP IDA rows on PA5495, sole seeds of the PTN001464661 IBDs, should be recoded IGI (process) and the MF re-anchored.
Q: Should PTN001464661 be restricted to type II homoserine kinases, excluding B. subtilis AmiN/YerI (amicoumacin kinase) and the uncharacterised Synechocystis sll1119 and Deinococcus DR_0394?
Experiment: Purify PA5495 and measure ATP-dependent homoserine phosphorylation (kinetics, nucleotide and substrate specificity), and test B. subtilis AmiN for homoserine kinase activity, to anchor the type II HSK node on direct evidence.
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