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

Abstract

Current textbook knowledge holds that the structural scope of ribosomal biosynthesis is based exclusively on α-amino acid backbone topology. Here we report the genome-guided discovery of bacterial pathways that posttranslationally create β-amino acid-containing products. The transformation is widespread in bacteria and is catalyzed by an enzyme belonging to a previously uncharacterized radical <i>S</i>-adenosylmethionine family. We show that the β-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 β-amino acids into genetically encoded precursors in <i>Escherichia coli</i> 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.