The first committed biosynthetic step toward clavulanic acid, the clinically important β- lactamase inhibitor, is catalyzed by the thiamin diphosphate (ThDP)-dependent enzyme N 2- (2-carboxyethyl) arginine synthase (CEAS). This protein carries out a unique reaction among ThDP-dependent processes in which a CN bond is formed, and an electrophilic acryloyl-thiazolium intermediate of ThDP is proposed to be involved, unlike the ...