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|Author(s):||S G. Codreanu; Jane E. Ladner; G Xiao; N V. Stourman; D L. Hachey; G L. Gilliland; R N. Armstrong;|
|Title:||Local Protein Dynamics and Catalysis: Detection of Segmental Motion Associated With Rate-Limiting Product Release by a Glutathione Transferase|
|Published:||December 24, 2002|
|Abstract:||Glutathione transferase rGSTM1-1 catalyzes the addition of glutathione (GSH) to 1-chloro-2,4-dinitrobenzene in which chemical step of the reaction 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 kcat (72 s-1) that is 3.6-fold larger than the native enzyme (20 s-1). Crystallographic observations and evidence from amide proton exchange kinetics are consistent with localized increases in 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 are 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 of about 3 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|
|Pages:||pp. 15161 - 15172|
|Keywords:||enzyme catalysis,enzyme dynamics,glutahione transferase,protein structure|
|Research Areas:||Chemical Analysis, Life Sciences Research|