期刊
ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS
卷 493, 期 1, 页码 3-12出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.abb.2009.07.001
关键词
Enzyme mechanism; Enzyme activation; Protein structure; Crystallography; Kinetic simulation; Proton relay; Zinc coordination
资金
- National Institutes of Health [GM078446]
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM078446] Funding Source: NIH RePORTER
As shown by X-ray crystallography, horse liver alcohol dehydrogenase undergoes a global conformational change upon binding of NAD(+) or NADH, involving a rotation of the catalytic domain relative to the coenzyme binding domain and the closing Lip Of the active site to produce a catalytically efficient enzyme. The conformational change requires a complete coenzyme and is affected by various chemical or mutational Substitutions that can increase the catalytic turnover by altering the kinetics of the isomerization and rate of dissociation of coenzymes. The binding of NAD(+) is kinetically limited by a unimolecular isomerization (corresponding to the conformational change) that is controlled by deprotonation of the catalytic zinc-water to produce a negatively-charged zinc-hydroxide, which can attract the positively-charged nicotinamide ring. The deprotonation is facilitated by His-51 acting through a hydrogen-bonded network to relay the proton to solvent. Binding of NADH also involves a conformational change, but the rate is very fast. After the enzyme binds NAD(+) and closes up, the substrate displaces the hydroxide bound to the catalytic zinc; this exchange may involve a double displacement reaction where the carboxylate group of a glutamate residue first displaces the hydroxide (inverting the tetrahedral coordination of the zinc). and then the exogenous ligand displaces the glutamate. The resulting enzyme-NAD(+)-alcoholate complex is poised for hydrogen transfer, and small conformational fluctuations may bring the reactants together so that the hydride ion is transferred by quantum mechanical tunneling. In the process, the nicotinamide ring may become puckered, as seen in structures of complexes of the enzyme with NADH. The conformational changes of alcohol dehydrogenase demonstrate the importance of protein dynamics in catalysis. (C) 2009 Elsevier Inc. All rights reserved.
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