Local protein dynamics and catalysis: detection of segmental motion associated with rate-limiting product release by a glutathione transferase.
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.
Codreanu
Simona G
SG
Department of Chemistry and Biochemistry, Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
Ladner
Jane E
JE
Xiao
Gaoyi
G
Stourman
Nina V
NV
Hachey
David L
DL
Gilliland
Gary L
GL
Armstrong
Richard N
RN
D000577:Amides / Q000737:chemistry; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D002384:Catalysis; D002942:Circular Dichroism; D003460:Crystallization; D018360:Crystallography, X-Ray; D017666:Deuterium Oxide / Q000737:chemistry; D004137:Dinitrochlorobenzene / Q000737:chemistry / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine / Q000235:genetics; D011487:Protein Conformation; D011522:Protons; D051381:Rats; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000235:genetics; D013816:Thermodynamics; D014443:Tyrosine / Q000235:genetics
D000577:Amides; D004137:Dinitrochlorobenzene; D011522:Protons; D014443:Tyrosine; D010649:Phenylalanine; D005982:Glutathione Transferase; D017666:Deuterium Oxide