N-Terminal Methionine Processing

Protein synthesis is initiated by methionine in eukaryotes and by formylmethionine in prokaryotes. N-terminal methionine can be co-translationally cleaved by the enzyme methionine aminopeptidase (MAP). When recombinant proteins are expressed in bacterial and mammalian expression systems, there is a simple universal rule that predicts whether the initiating methionine will be processed by MAP based on the size of the residue adjacent (penultimate) to the N-methionine. In general, if the side chains of the penultimate residues have a radius of gyration of 1.29 Å or less, methionine is cleaved. © 2017 by John Wiley & Sons, Inc.