3ljp
Crystal structure of choline oxidase V464A mutant
Structural highlights
FunctionCHOX_ARTGO Catalyzes the two-step oxidative conversion of choline to glycine-betaine with betaine aldehyde as an intermediate. Glycine-betaine accumulates to high levels in the cytoplasm of cells to prevent dehydration and plasmolysis in adverse hyperosmotic environments. Accepts either choline or the reaction intermediate betaine-aldehyde as substrate.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe oxidation of reduced flavin cofactors by oxygen is a very important reaction that is central to the chemical versatility of hundreds of flavoproteins classified as monooxygenases and oxidases. These enzymes are characterized by bimolecular rate constants >/=10(5) M(-1) s(-1) and produce water and hydrogen peroxide, respectively. A hydrophobic cavity close to the reactive flavin C(4a) atom has been previously identified in the 3D structure of monooxygenases but not in flavoprotein oxidases. In the present study, we have investigated by X-ray crystallography, mutagenesis, steady-state, and rapid reaction approaches the role of Val464, which is <6 A from the flavin C(4a) atom in choline oxidase. The 3D structure of the Val464Ala enzyme was essentially identical to that of the wild-type enzyme as shown by X-ray crystallography. Time-resolved anaerobic substrate reduction of the enzymes showed that replacement of Val464 with alanine or threonine did not affect the reductive half-reaction. Steady-state and rapid kinetics as well as enzyme-monitored turnovers indicated that the oxidative half-reaction in the Ala464 and Thr464 enzymes was decreased by approximately 50-fold with respect to the wild-type enzyme. We propose that the side chain of Val464 in choline oxidase provides a nonpolar site that is required to guide oxygen in proximity of the C(4a) atom of the flavin, where it will subsequently react via electrostatic catalysis. Visual analysis of available structures suggests that analogous nonpolar sites are likely present in most flavoprotein oxidases. Mechanistic considerations provide rationalization for the differences between sites in monooxygenases and oxidases. Role of Valine 464 in the Flavin Oxidation Reaction Catalyzed by Choline Oxidase (,).,Finnegan S, Agniswamy J, Weber IT, Gadda G Biochemistry. 2010 Mar 10. PMID:20184377[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
| ||||||||||||||||||||
