Mechanistic Implications of the Deamination of TDP-4-amino-4-deoxy-d-fucose Catalyzed by the Radical SAM Enzyme DesII.

ABSTRACT: DesII is a radical SAM lyase that catalyzes a deamination reaction during the biosynthesis of desosamine in Streptomyces venezuelae. Competing mechanistic hypotheses for this radical-mediated reaction are differentiated according to whether a 1,2-migration takes place and the timing of proton abstraction following generation of a substrate ?-hydroxyalkyl radical intermediate. In this study, the deuterated C4 epimer of the natural substrate, TDP-4-amino-4-deoxy-d-[3-2H]fucose, was prepared and shown to be a substrate for DesII undergoing deamination alone with a specific activity that is only marginally reduced (?3-fold) with respect to that of deamination of the natural substrate. Furthermore, pH titration of the deamination reaction implicates the presence of a hydron acceptor that facilitates catalysis but does not appear to be necessary. On the basis of these as well as previously reported results, a mechanism involving direct elimination of ammonium with concerted proton transfer to the nucleofuge from the adjacent ?-hydroxyalkyl radical is proposed.

SUBMITTER: Ko Y 

PROVIDER: S-EPMC5988952 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature