PA5542 (named PIB-1) is a 414-residue chromosomally encoded beta-lactamase of Pseudomonas aeruginosa with a predicted N-terminal signal peptide and a single Beta-lactamase/transpeptidase-like domain (Pfam PF00144) that carries the S-x-x-K active-site motif of the serine penicillin-recognising enzymes. The purified enzyme hydrolyses imipenem and other carbapenems but not cephalosporins, and its activity rises in the presence of metal ions, especially zinc, which promote formation of more active trimers rather than binding at the active site. Crystal structures place it in class C beta-lactamases, as the founder of a divergent, metal-stimulated subgroup. PA5542 belongs to the P. aeruginosa core genome; its loss increases carbapenem susceptibility and its overexpression lowers carbapenem susceptibility in Escherichia coli, so it contributes to intrinsic carbapenem resistance.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008800 beta-lactamase activity | IDA PMID:25185138 Characterization of a novel ZnΒ²βΊ-dependent intrinsic imipene... | ACCEPT | Summary: PseudoCAP row and a seed of the PTN009168613 hydrolase activity IBD. The purified enzyme hydrolyses imipenem in a spectrophotometric assay. Reason: Direct assay of purified protein, confirmed and extended by the 2024 structural and functional study (carbapenems hydrolysed, cephalosporins not). Beta-lactamase activity is the core molecular function; GO has no narrower carbapenemase term. Supporting Evidence: PMID:25185138 Spectrophotometric analyses showed that PA5542 is a Zn(2+)-dependent imipenemase. PMID:39097051 Functional analysis showed that PIB-1 is able to degrade carbapenems but not cephalosporins, the typical substrate of Class C Ξ²-lactamases, and that its catalytic activity increases in the presence of metal ions, especially zinc. |
| GO:0016787 hydrolase activity | IBA GO_REF:0000033 | TOO GENERAL | Summary: IBA from PTN009168613, seeded by PA5542 itself, E. coli PBP4B/YfeW (P77619, IDA D-alanyl-D-alanine carboxypeptidase) and B. subtilis AmiE/YbbE (O05213, EXP amidase). The generic node term is true for PA5542. Reason: True but entailed by the accepted GO:0008800 beta-lactamase activity, which is_a hydrolase activity. The node term is suitably generic for a PF00144 clade of penicillin-binding-fold hydrolases with different substrates, and the IBD stands on the two other seeds. |
| GO:0046677 response to antibiotic | IMP PMID:25185138 Characterization of a novel ZnΒ²βΊ-dependent intrinsic imipene... | KEEP AS NON CORE | Summary: PseudoCAP row from the knockout susceptibility phenotype: loss of PA5542 increases carbapenem susceptibility. Reason: The phenotype reflects antibiotic inactivation by the enzyme, not a response to an antibiotic stimulus, but GO practice uses this term for resistance determinants and the same convention is followed in other P. aeruginosa reviews here (ampR, mexZ, pmpM). The specific process is captured by carbapenem catabolic process. Supporting Evidence: PMID:25185138 Lack of PA5542 increases P. aeruginosa 59.20 susceptibility to carbapenems and its overexpression reduces E. coli susceptibility to these Ξ²-lactams. |
| GO:1901768 carbapenem catabolic process | IMP PMID:25185138 Characterization of a novel ZnΒ²βΊ-dependent intrinsic imipene... | ACCEPT | Summary: PseudoCAP row. PA5542 hydrolyses the beta-lactam ring of carbapenems, which is carbapenem breakdown. Reason: The enzyme itself catalyses the step (hydrolysis of imipenem and meropenem), so it does the work of the process; the mutant susceptibility phenotype is consistent with this. This is the biological-process counterpart of the core activity. Supporting Evidence: PMID:25185138 Spectrophotometric analyses showed that PA5542 is a Zn(2+)-dependent imipenemase. PMID:39097051 Functional analysis showed that PIB-1 is able to degrade carbapenems but not cephalosporins, the typical substrate of Class C Ξ²-lactamases, and that its catalytic activity increases in the presence of metal ions, especially zinc. |
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Download this section (compressed HTML)Q: Is PIB-1 periplasmic as its predicted signal peptide implies, and does its trimerisation occur at physiological zinc concentrations in the periplasm?
Experiment: Cell fractionation of P. aeruginosa expressing tagged PIB-1, with kinetic comparison of carbapenem hydrolysis by monomeric and trimeric enzyme across zinc concentrations.
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