Deletion of the pyc Gene Blocks Clavulanic Acid Biosynthesis Except in Glycerol-Containing Medium: Evidence for Two Different Genes in Formation of the C3 Unit

摘要: Clavulanic acid, a clinically used β-lactamase inhibitor, is synthesized by condensation of arginine (25, 29) with C3 unit derived from pyruvate or glycerate. Incorporation labelled glycerate into clavulanic acid has been reported (9, 28), but the nature intermediate substrate that binds to amino group remains uncertain. Gutman et al. (12) proposed an intact incorporation β-hydroxypropionate based on unchanged 3H/14C ratio in following double-labelled [2-3H, 2-14C]hydroxypropionate, which suggests no tritium lost C-2 methylene during unit. The oxidation levels carbon atoms are same as those acid. Townsend and Ho showed precursor (28), use would require removal hydroxyl at 2 glycerate, not present β-lactam ring acid. Feeding experiments using racemic [1,2-13C, 2,3,3,-2H] hydrogen C-6 occurred (23). Recently Thirkettle (27) (and glycerate) most likely primary metabolic source three carbons However, reactions required convert remain unknown. utilization does exclude involvement final reaction. The genes for biosynthesis clustered together cephamycin C biosynthesis, forming so-called supercluster (14, 30). Several cluster (cas2, bls, pah, car, claR) have assigned specific roles (1, 2, 17, 19, 22), encoding formation initial step results N-carboxyethylarginine (10) be identified. Since involved sometimes associated clusters (18), it great interest characterize and/or unit. We identified gene, pyc, encodes protein ressembling acetohydroxyacid synthases appears conversion Inactivation this gene leads inability produce starch-asparagine medium GSPG (glycerol, glutamic proline) medium, suggesting alternative pathway bypasses