title: Mechanistic studies of the radical S-adenosyl-L-methionine enzyme DesII: EPR characterization of a radical intermediate generated during its catalyzed dehydrogenation of TDP-D-quinovose.
abstract: DesII, a radical S-adenosyl-l-methionine (SAM) enzyme from Streptomyces venezuelae, catalyzes the deamination of TDP-4-amino-4,6-dideoxy-D-glucose to TDP-3-keto-4,6-dideoxy-D-glucose in the desosamine biosynthetic pathway. DesII can also catalyze the dehydrogenation of TDP-D-quinovose to the corresponding 3-keto sugar. Similar to other radical SAM enzymes, DesII catalysis has been proposed to proceed via a radical mechanism. This hypothesis is now confirmed by EPR spectroscopy with the detection of a TDP-D-quinovose radical intermediate having a g-value of 2.0025 with hyperfine coupling to two spin 1/2 nuclei, each with a splitting constant of 33.6 G. A significant decrease in the EPR line width is observed when the radical is generated in reactions conducted in D(2)O versus H(2)O. These results are consistent with a C3 α-hydroxyalkyl radical in which the p-orbital harboring the unpaired electron spin at C3 is periplanar with the C-H bonds at both C2 and C4.
authors.affiliation: Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Ruszczycky
authors.forename: Sei-hyun
authors.initials: SH
authors.lastname: Choi
authors.forename: Steven O
authors.initials: SO
authors.lastname: Mansoorabadi
authors.forename: Hung-wen
authors.initials: HW
authors.lastname: Liu
mesh_terms: D055162:Biocatalysis; D002240:Carbohydrate Sequence; D003847:Deoxyglucose / Q000031:analogs & derivatives* / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006865:Hydrogenation; D008969:Molecular Sequence Data; D012436:S-Adenosylmethionine / Q000737:chemistry*; D013302:Streptomyces / Q000201:enzymology
chemical_list: D005609:Free Radicals; D012436:S-Adenosylmethionine; D003847:Deoxyglucose; C037904:6-deoxyglucose