Mechanistic studies of thioether crosslink formation in peptides

PROJECT SUMMARYAll domains of life produce peptidic natural products that play roles as diverse as quorumsensing molecules and redox cofactors. The ability of these peptides to function asantibacterial, antiviral, or anticancer agents makes understanding their biosynthesis animportant area of contemporary research. Peptide-based secondary metabolites areproduced by distinct biosynthetic pathways that differ in whether the peptide issynthesized by the action of non-ribosomal peptide synthetases (NRPS), or ribosomallyproduced from a genomically encoded orf. These peptides are often extensivelymodified. While in the NRPS systems many of the modifications occur concurrently withpeptide synthesis, the ribosomally encoded peptides undergo posttranslationalmodification. These so-called ribosomally encoded posttranslationally modifiedpolypeptides (RiPP) are a new emerging class of polypeptides that have extensivemodifications that are introduced by mechansims that are mostly poorly understood.This application will focus on enzymes introduce sulfur-to-alpha carbon thioethercrosslinks into ribosomally encoded peptides to produce sactipeptides. These linkagesare distinct from the well-studied lanthipeptide, where thioether crosslinks form betweena Cys residue and a dehydrated Thr/Ser. The sactipeptide maturases are members ofthe radical SAM family of enzymes and catalyze thioether crosslinks by a radical-mediated reaction that is not understood. While The biochemical, spectroscopic, andstructural studies in this application will lead to a mechanistic paradigm for this importantclass of enzymes. While sactipeptides themselves have various therapeutic uses,understanding the substrate profiles and mechanisms of these enzymes would provide atool for synthesis of crosslinked peptides, which are increasing finding utility in the clinic.