An Orthogonal D 2 O-Based Induction System that Provides Insights into d -Amino Acid Pattern Formation by Radical S-Adenosylmethionine Peptide Epimerases

International audienceRadical S-adenosyl methionine peptide epimerases (RSPEs) are an enzyme family that accomplishes regiospecific and irreversible introduction of multiple d-configured residues into ribosomally encoded peptides. Collectively, RSPEs can generate diverse epimerization patterns in a wide range of substrates. Previously, the lack of rapid methods to localize epimerized residues has impeded efforts to investigate the function and applicative potential of RSPEs. An efficient mass spectrometry-based assay is introduced that permits characterization of products generated in E. coli. Applying this to a range of non-natural peptide-epimerase combinations, it is shown that the d-amino acid pattern is largely but not exclusively dictated by the core peptide sequence, while the epimerization order is dependent on the enzyme-leader pair. RSPEs were found to be highly promiscuous, which allowed for modular introduction of peptide segments with defined patterns

Natural noncanonical protein splicing yields products with diverse b-amino acid residues

International audienceCurrent textbook knowledge holds that the structural scope of ribosomal biosynthesis is based exclusively on a-amino acid backbone topology. Here we report the genome-guided discovery of bacterial pathways that posttranslationally create b-amino acid-containing products. The transformation is widespread in bacteria and is catalyzed by an enzyme belonging to a previously uncharacterized radical S-adenosylmethionine family. We show that the b-amino acids result from an unusual protein splicing process involving backbone carbon-carbon bond cleavage and net excision of tyramine. The reaction can be used to incorporate diverse and multiple b-amino acids into genetically encoded precursors in Escherichia coli. In addition to enlarging the set of basic amino acid components, the excision generates keto functions that are useful as orthogonal reaction sites for chemical diversification

Widespread microbial utilization of ribosomal β-amino acid-containing peptides and proteins

β-Amino residues are regarded as extremely rare features among ribosomal products. They can be installed by a remarkable non-canonical enzymatic splicing process occurring in some Nif11-type ribosomally synthesized and posttranslationally modified peptide (RiPP) pathways from select cyanobacteria. The functions of the final pathway products remained unknown. Here, a global bioinformatic analysis suggested an unexpectedly broad distribution of ribosomal β-amino acid products in diverse bacterial lineages as well as archaea. Characterization of 27 bacterial splicease-substrate pairs confirmed the modification in all cases. The “spliceotide” products include many previously unrecognized RiPP types as well as proteins, contain 35 to >600 residues, and feature single to multiple α-keto-β-amino acid moieties, with 15 different naturally occurring β units characterized and 20 predicted. Of three tested spliceotides, all exhibited exceptionally potent protease inhibitory activity, providing a potential rationale for the widespread splicease chemistry in prokaryotes and highlighting substantial potential for drug discovery and gene-based biomolecule diversification.ISSN:2451-9294ISSN:2451-930