Local protein dynamics and catalysis: Detection of segmental motion associated with rate-limiting product release by a glutathione transferase

被引:34
作者
Codreanu, SG
Ladner, JE
Xiao, GY
Stourman, NV
Hachey, DL
Gilliland, GL
Armstrong, RN
机构
[1] Vanderbilt Univ, Sch Med, Ctr Mol Toxicol, Dept Chem, Nashville, TN 37232 USA
[2] Vanderbilt Univ, Sch Med, Ctr Mol Toxicol, Dept Biochem, Nashville, TN 37232 USA
[3] Univ Maryland, Ctr Adv Res Biotechnol, Maryland Biotechnol Inst, Shady Grove, MD USA
[4] NIST, Rockville, MD 20850 USA
关键词
D O I
10.1021/bi026776p
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Glutathione transferase rGSTM1-1 catalyzes the addition of glutathione (GSH) to 1-chloro-2,4-dinitrobenzene, a reaction in which the chemical step is 60-fold faster than the physical step of product release. The hydroxyl group of Y115, located in the active site access channel, controls the egress of product from the active site. The Y115F mutant enzyme has a k(cat) (72 s(-1)) that is 3.6-fold larger than that of the native enzyme (20 s(-1)). Crystallographic observations and evidence from amide proton exchange kinetics are consistent with localized increases in the degree of segmental motion of the Y115F mutant that are coupled to the enhanced rate of product release. The loss of hydrogen bonding interactions involving the hydroxyl group of Y115 is reflected in subtle alterations in the backbone position, an increase in B-factors for structural elements that comprise the channel to the active site, and, most dramatically, a loss of well-defined electron density near the site of mutation. The kinetics of amide proton exchange are also enhanced by a factor between 3 and 12 in these regions, providing direct, quantitative evidence for changes in local protein dynamics affecting product release. The enhanced product release rate is proposed to derive from a small shift in the equilibrium population of protein conformers that permit egress of the product from the active site.
引用
收藏
页码:15161 / 15172
页数:12
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