SpuB (PA0298, PauA2) is a glutamine synthetase-like gamma-glutamylpolyamine synthetase of Pseudomonas aeruginosa PAO1, encoded in the polyamine-inducible spuABCDEFGH operon and homologous to Escherichia coli PuuA, the gamma-glutamylputrescine synthetase that starts the gamma-glutamylation route from polyamines to GABA. SpuB is the only one of the seven PauA paralogs whose single loss blocks growth on spermidine, so it is thought to be the spermidine-glutamylating enzyme; it also contributes, with PauA1 and PauA4, to putrescine utilization. Its activity has not been assayed with purified protein.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO from the GS/guanido kinase catalytic domain. Reason: Entailed by GO:0016880 acid-ammonia (or amide) ligase activity, the core function MF. |
| GO:0004356 glutamine synthetase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from GS domain signatures, which do not separate glutamine synthetases from gamma-glutamylpolyamine synthetases. Reason: Reaction class right, substrate wrong. SpuB/PauA2 is a PuuA-family enzyme required for spermidine utilization; GlnA is the P. aeruginosa glutamine synthetase. GO has no glutamate-spermidine ligase term and the substrate is unassayed, so generalize to the parent class. Proposed replacements: acid-ammonia (or amide) ligase activity Supporting Evidence: file:PSEAE/spuB/spuB-uniprot.txt PANTHER; PTHR43785; GAMMA-GLUTAMYLPUTRESCINE SYNTHETASE; 1. |
| GO:0006598 polyamine catabolic process | IBA GO_REF:0000033 | TOO GENERAL | Summary: IBA from PTN001839150 seeded by E. coli PuuA, PA1566/PauA3, SpuI/PauA1 and SpuB itself (expected, not circular). The IBD stands without this seed. Reason: Entailed by GO:0046203 spermidine catabolic process (is_a GO:0006598), accepted below. |
| GO:0016879 ligase activity, forming carbon-nitrogen bonds | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA ligase (C-N) activity. Reason: Entailed by GO:0016880 (is_a GO:0016879), the core function MF. |
| GO:0042402 biogenic amine catabolic process | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA biogenic amine catabolism. Reason: Entailed by GO:0046203 spermidine catabolic process, accepted below. |
| GO:0046203 spermidine catabolic process | IMP PMID:21622750 Functional characterization of seven Ξ³-Glutamylpolyamine syn... | ACCEPT | Summary: PseudoCAP seed row for PTN001839150. A single pauA2 knockout completely blocks growth on spermidine, and the earlier spuB transposon mutant was also defective in spermidine utilization. Seed verdict SOUND. Reason: Two independent mutant studies agree, and SpuB is the predicted first, gamma-glutamylating enzyme of the pathway, so it performs a step of the process rather than only being required for it. Supporting Evidence: PMID:21622750 The results revealed that it requires specific combinations of pauA knockouts to abolish utilization of different polyamines PMID:12081945 Although spuA and spuB mutants showed an apparent defect in spermidine utilization |
| GO:1901704 L-glutamine biosynthetic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA from the deep GS-family node PTN000464978 (seed B. subtilis GlnA). SpuB sits in the PuuA-like gamma-glutamylpolyamine synthetase clade. Reason: Over-propagation of the ancestral glutamine synthetase role to a substrate-diverged paralog that acts in spermidine catabolism; GlnA supplies glutamine in P. aeruginosa. Not REMOVE because residual glutamine synthesis has not been tested. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000464978 Β· PTN000464978 SUPPORTS SOURCE BUT NOT TARGET GS-family node; right for GlnA, not for the PuuA/PauA subclade. UniProtKB:P12425 Β· B. subtilis GlnA SUPPORTS SOURCE BUT NOT TARGET Bona fide glutamine synthetase. Supporting Evidence: file:PSEAE/spuB/spuB-uniprot.txt PANTHER; PTHR43785; GAMMA-GLUTAMYLPUTRESCINE SYNTHETASE; 1. |
| GO:1901704 L-glutamine biosynthetic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro2GO from the GS N-terminal domain superfamily. Reason: Same claim and reasoning as the IBA row. |
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Download this section (compressed HTML)Q: Does SpuB gamma-glutamylate spermidine directly, and at which amino group, or does it act on a spermidine-derived intermediate?
Experiment: Purify SpuB/PauA2 and measure ATP-dependent gamma-glutamylation of spermidine, putrescine and 1,3-diaminopropane, identifying the product by LC-MS.
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