Effect of mutagenesis on the stereochemistry of enoyl-CoA hydratase.
Enoyl-CoA hydratase catalyzes the hydration of trans-2-crotonyl-CoA to 3(S)-HB-CoA, 3(S)-hydroxybutyryl-CoA with a stereospecificity (k(S)/k(R)) of 400000 to 1 [Wu, W. J., Feng, Y., He, X., Hofstein, H. S., Raleigh, D. P., and Tonge, P. J. (2000) J. Am. Chem. Soc. 122, 3987-3994]. Replacement of E164, one of the catalytic glutamates in the active site, with either aspartate or glutamine reduces the rate of formation of the 3(S) product enantiomer (k(S)) without affecting the rate of formation of the 3(R) product (k(R)). Consequently, k(S)/k(R) is 1000 and 0.33 for E164D and E164Q, respectively. In contrast, mutagenesis of E144, the second catalytic glutamate, reduces the rate of formation of both product enantiomers. Thus, only E144 is required for the formation of 3(R)-HB-CoA, 3(R)-hydroxybutyryl-CoA. Modeling studies together with analysis of alpha-proton exchange rates and experiments with crotonyl-oxyCoA, a substrate analogue in which the alpha-proton acidity has been reduced 10000-fold, support a mechanism of 3(R)-hydroxybutyryl-CoA formation that involves the E144-catalyzed stepwise addition of water to crotonyl-CoA which is bound in an s-trans conformation in the active site. Finally, we also demonstrate that hydrogen bonds in the oxyanion hole, provided by the backbone amide groups of G141 and A98, are important for the formation of both product enantiomers.
Feng
Yuguo
Y
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA.
Hofstein
Hilary A
HA
Zwahlen
Jacque
J
Tonge
Peter J
PJ
D000214:Acyl Coenzyme A / Q000737:chemistry; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D004746:Enoyl-CoA Hydratase / Q000737:chemistry* / Q000235:genetics*; D018698:Glutamic Acid / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D011522:Protons; D051381:Rats; D013237:Stereoisomerism; D013379:Substrate Specificity
D000214:Acyl Coenzyme A; D011522:Protons; C434763:crotonyl-oxycoenzyme A; C030372:3-hydroxybutyryl-coenzyme A; D018698:Glutamic Acid; D004746:Enoyl-CoA Hydratase