Glutamine amidotransferases class-II (GATase) asparagine synthase_betaLS-type. Carbapenam synthetase (CarA) is an ATP/Mg2+-dependent enzyme that catalyzes the formation of the beta-lactam ring in (5R)-carbapenem-3-carboxylic acid biosynthesis. CarA is homologous to beta-lactam synthetase (beta-LS), which is involved in the biosynthesis of clavulanic acid, a clinically important beta-lactamase inhibitor. CarA and beta-LS each have two distinct domains, an N-terminal Ntn hydrolase domain and a C-terminal synthetase domain, a domain architecture similar to that of the class-B asparagine synthetases (AS-B's). The N-terminal domain of these enzymes hydrolyzes glutamine to glutamate and ammonia. CarA forms a homotetramer while betaLS forms a heterodimer. The N-terminal folds of CarA and beta-LS are similar to those of other class II glutamine amidotransferases including lucosamine-fructose 6-phosphate synthase (GLMS or GFAT), glutamine phosphoribosylpyrophosphate (Prpp) amidotransferase (GPATase), asparagine synthetase B (AsnB), and glutamate synthase (GltS). This fold is also somwhat similar to the Ntn (N-terminal nucleophile) hydrolase fold of the proteasomal alpha and beta subunits.
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