Biomimetic Catalysis of Intermodular Aminoacyl Transfer

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Abstract
Intermodular aminoacyl transfer is the fundamental bond-forming reaction in the biosynthesis of polypeptides by ribosomes and nonribosomal peptide synthetases (NRPS). Here we report the design and functional characterizations of short synthetic α-helical peptides that mimic the aminoacyl loading and intermodular aminoacyl transfer steps of NRPS with aminolysis rate enhancements in neutral aqueous solutions of up to 5400-fold (kcat/kuncat). The catalysts operate as noncovalently associated peptide assemblies with composite active sites fashioned at the interface between helical subunits. Following the substrate loading at the active site cysteine, the juxtaposition of the resulting aminoacyl thiolester and the nucleophilic amine of the acyl acceptor moiety gives rise to high effective concentrations (up to 54 M) that facilitate interhelical aminoacyl transfer with rates typically exceeding 10-4 sec-1. Moreover, studies based on homo- and heteromeric assemblies, active site amino acid substitutions, kinetic analysis, and reaction modeling indicate that the de novo designed supramolecular catalysts reported herein exhibit some of the basic characteristics of natural enzymes, including precise positioning and pKa modulation of active site residues, covalent catalysis, and multiple product turnovers.