Fig. 1.

Nocardicin biosynthetic pathway. a Nocardicin biosynthesis is initiated through the activities of five modules spanning two proteins, NocA and NocB. The final steps in the release of the pro-nocardicin G pentapeptide are carried out by the bifunctional thioesterase domain (NocTE), which catalyzes both epimerization of the C-terminal Hpg residue and hydrolysis. b Whereas diphenylphosphonate analogs did not react with the catalytic nucleophile of the thioesterase domain, a fluorophosphonate tripeptide analog 4 inactivated the enzyme and was used in structural studies to characterize the active site