Stoichiometry of the redox neutral deamination and oxidative dehydrogenation reactions catalyzed by the radical SAM enzyme DesII.
DesII from Streptomyces venezuelae is a radical SAM (S-adenosyl-l-methionine) enzyme that catalyzes the deamination of TDP-4-amino-4,6-dideoxy-d-glucose to form TDP-3-keto-4,6-dideoxy-d-glucose in the biosynthesis of TDP-d-desosamine. DesII also catalyzes the dehydrogenation of the nonphysiological substrate TDP-D-quinovose to TDP-3-keto-6-deoxy-d-glucose. These properties prompted an investigation of how DesII handles SAM in the redox neutral deamination versus the oxidative dehydrogenation reactions. This work was facilitated by the development of an enzymatic synthesis of TDP-4-amino-4,6-dideoxy-d-glucose that couples a transamination equilibrium to the thermodynamically favorable oxidation of formate. In this study, DesII is found to consume SAM versus TDP-sugar with stoichiometries of 0.96 +/- 0.05 and 1.01 +/- 0.05 in the deamination and dehydrogenation reactions, respectively, using Na(2)S(2)O(4) as the reductant. Importantly, no significant change in stoichiometry is observed when the flavodoxin/flavodoxin NADP(+) oxidoreductase/NADPH reducing system is used in place of Na(2)S(2)O(4). Moreover, there is no evidence of an uncoupled or abortive process in the deamination reaction, as indicated by the observation that dehydrogenation can take place in the absence of an external source of reductant whereas deamination cannot. Mechanistic and biochemical implications of these results are discussed.
Ruszczycky
Mark W
MW
Division of Medicinal Chemistry, College of Pharmacy, and Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Choi
Sei-Hyun
SH
Liu
Hung-Wen
HW
D002384:Catalysis; D003641:Deamination; D006865:Hydrogenation; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D009700:Nucleoside Deaminases / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry* / Q000378:metabolism; D013302:Streptomyces / Q000201:enzymology
D007506:Iron-Sulfur Proteins; D012436:S-Adenosylmethionine; D010088:Oxidoreductases; D009700:Nucleoside Deaminases