Structures of two distinct conformations of holo-non-ribosomal peptide synthetases

X-ray crystal structures of two distinct steps in the catalytic cycle of non-ribosomal peptide synthetases are described, offering the potential to generate novel products through engineering enzyme activity. Non-ribosomal peptides, such as the antibiotic vancomycin and the immunosuppressant cyclosporin A, are peptidic secondary metabolites produced by microorganisms. Non-ribosomal peptide synthetases (NRPSs) are a family of large enzymes that utilize multiple catalytic domains to catalyse sequential steps in the biosynthetic pathway of this family of 'natural products'. Two papers in this issue of Nature present X-ray crystal structures that indicate that NRPSs are substantially more dynamic than previously believed. Andrew Gulick and colleagues studied two holo-non-ribosomal peptide synthetase modules, each revealing a distinct step in the catalytic cycle. Martin Schmeing and colleagues report several structures of LgrA, which is involved in the biosynthesis of the antibiotic gramicidin. Many important natural products are produced by multidomain non-ribosomal peptide synthetases (NRPSs)1,2,3,4. During synthesis, intermediates are covalently bound to integrated carrier domains and transported to neighbouring catalytic domains in an assembly line fashion5. Understanding the structural basis for catalysis with non-ribosomal peptide synthetases will facilitate bioengineering to create novel products. Here we describe the structures of two different holo-non-ribosomal peptide synthetase modules, each revealing a distinct step in the catalytic cycle. One structure depicts the carrier domain cofactor bound to the peptide bond-forming condensation domain, whereas a second structure captures the installation of the amino acid onto the cofactor within the adenylation domain. These structures demonstrate that a conformational change within the adenylation domain guides transfer of intermediates between domains. Furthermore, one structure shows that the condensation and adenylation domains simultaneously adopt their catalytic conformations, increasing the overall efficiency in a revised structural cycle. These structures and the single-particle electron microscopy analysis demonstrate a highly dynamic domain architecture and provide the foundation for understanding the structural mechanisms that could enable engineering of novel non-ribosomal peptide synthetases.