title: β-Lactam formation by a non-ribosomal peptide synthetase during antibiotic biosynthesis.
abstract: Non-ribosomal peptide synthetases are giant enzymes composed of modules that house repeated sets of functional domains, which select, activate and couple amino acids drawn from a pool of nearly 500 potential building blocks. The structurally and stereochemically diverse peptides generated in this manner underlie the biosynthesis of a large sector of natural products. Many of their derived metabolites are bioactive such as the antibiotics vancomycin, bacitracin, daptomycin and the β-lactam-containing penicillins, cephalosporins and nocardicins. Penicillins and cephalosporins are synthesized from a classically derived non-ribosomal peptide synthetase tripeptide (from δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase). Here we report an unprecedented non-ribosomal peptide synthetase activity that both assembles a serine-containing peptide and mediates its cyclization to the critical β-lactam ring of the nocardicin family of antibiotics. A histidine-rich condensation domain, which typically performs peptide bond formation during product assembly, also synthesizes the embedded four-membered ring. We propose a mechanism, and describe supporting experiments, that is distinct from the pathways that have evolved to the three other β-lactam antibiotic families: penicillin/cephalosporins, clavams and carbapenems. These findings raise the possibility that β-lactam rings can be regio- and stereospecifically integrated into engineered peptides for application as, for example, targeted protease inactivators.
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Gaudelli
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Darcie H
authors.initials: DH
authors.lastname: Long
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Townsend
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000737:chemistry*; D055162:Biocatalysis; D053898:Biosynthetic Pathways; D003500:Cyclization; D006639:Histidine; D007769:Lactams / Q000737:chemistry* / Q000378:metabolism*; D010453:Peptide Synthases / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D047090:beta-Lactams / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D007769:Lactams; D047090:beta-Lactams; D012694:Serine; D006639:Histidine; C027318:nocardicin; D010453:Peptide Synthases