Identification and Characterization of the Sulfazecin Monobactam Biosynthetic Gene Cluster.

ABSTRACT: The monobactams, exemplified by the natural product sulfazecin, are the only class of ?-lactam antibiotics not inactivated by metallo-?-lactamases, which confer bacteria with extended-spectrum ?-lactam resistance. We screened a transposon mutagenesis library from Pseudomonas acidophila ATCC 31363 and isolated a sulfazecin-deficient mutant that revealed a gene cluster encoding two non-ribosomal peptide synthetases (NRPSs), a methyltransferase, a sulfotransferase, and a dioxygenase. Three modules and an aberrant C-terminal thioesterase (TE) domain are distributed across the two NRPSs. Biochemical examination of the adenylation (A) domains provided evidence that L-2,3-diaminopropionate, not L-serine as previously thought, is the direct source of the ?-lactam ring of sulfazecin. ATP/PPi exchange assay also revealed an unusual substrate selectivity shift of one A domain when expressed with or without the immediately upstream condensation domain. Gene inactivation analysis defined a cluster of 13 open reading frames sufficient for sulfazecin production, precursor synthesis, self-resistance, and regulation. The identification of a key intermediate supported a proposed NRPS-mediated mechanism of sulfazecin biosynthesis and ?-lactam ring formation distinct from the nocardicins, another NRPS-derived subclass of monocyclic ?-lactam. These findings will serve as the basis for further biosynthetic research and potential engineering of these important antibiotics.

SUBMITTER: Li R 

PROVIDER: S-EPMC5286544 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature