Ni2+-activated glyoxalase I from Escherichia coli: Substrate specificity, kinetic isotope effects and evolution within the βαβββ superfamily
作者:Kadia Y. Mullings、Nicole Sukdeo、Uthaiwan Suttisansanee、Yanhong Ran、John F. Honek
DOI:10.1016/j.jinorgbio.2011.11.008
日期:2012.3
The Escherichia coli glyoxalase system consists of the metalloenzymes glyoxalase I and glyoxalase II. Little is known regarding Ni2+-activated E. coli glyoxalase I substrate specificity, its thiol cofactor preference, the presence or absence of any substrate kinetic isotope effects on the enzyme mechanism, or whether glyoxalase I might catalyze additional reactions similar to those exhibited by related beta alpha beta beta beta structural superfamily members. The current investigation has shown that this two-enzyme system is capable of utilizing the thiol cofactors glutathionylspermidine and trypanothione, in addition to the known tripeptide glutathione, to convert substrate methylglyoxal to non-toxic D-lactate in the presence of Ni2+ ion. E. coli glyoxalase I, reconstituted with either Ni2+ or Cd2+, was observed to efficiently process deuterated and non-deuterated phenylglyoxal utilizing glutathione as cofactor. Interestingly, a substrate kinetic isotope effect for the Ni2+-substituted enzyme was not detected; however, the proton transfer step was observed to be partially rate limiting for the Cd2+-substituted enzyme. This is the first non-Zn2+-activated GlxI where a metal ion-dependent kinetic isotope effect using deuterium-labelled substrate has been observed. Attempts to detect a glutathione conjugation reaction with the antibiotic fosfomycin, similar to the reaction catalyzed by the related superfamily member FosA, were unsuccessful when utilizing the E. coli glyoxalase I E56A mutein. (c) 2011 Elsevier Inc. All rights reserved.