Four enzymes define the incorporation of coenzyme A in thienamycin biosynthesis

The enzymatic activities of three proteins encoded by the thienamycin gene cluster of Streptomyces cattleya (ThnR, ThnH, and ThnT) have been shown to incrementally cleave CoA to afford the active side-chain component of the beta-lactam antibiotic thienamycin. These results supersede proposals based on earlier radiochemical incorporation experiments. For 20 years it has been thought that cysteine was directly incorporated into the antibiotic. Specific, stepwise truncation of CoA to 4-phosphopantetheine, pantetheine, and finally cysteamine was observed with ThnR, ThnH, and ThnT, respectively, in a series of coupled enzymatic assays. Pantetheinylated carbapenams were synthesized to address possible thienamycin biosynthetic intermediates and were shown to be effective substrates for the pantetheine-cleaving enzyme ThnT. Finally, a fourth gene, thnF, was shown to encode a protein capable of N-acetylating a model compound containing cysteamine in the presence of acetyl-CoA, consistent with the production of the S. cattleya cometabolite, N-acetylthienamycin. Taken together, these four enzymes are proposed to siphon CoA from primary metabolism to create the side chains for the predominant S. cattleya carbapenems, thienamycin and N-acetylthienamycin, in a process likely to be general for the broader class of these antibiotics.