tailieunhanh - Báo cáo khoa học: Probing the catalytic potential of the hamster arylamine N-acetyltransferase 2 catalytic triad by site-directed mutagenesis of the proximal conserved residue, Tyr190

ArylamineN-acetyltransferases (NATs) play an important role in both the detoxification of arylamine and hydrazine drugs and the activation of aryl-amine carcinogens. Because the catalytic triad, Cys-His-Asp, of mammalian NATs has been shown to be essential for maintaining protein stability, ren-dering it impossible to assess alterations of the triad on catalysis, we explored the impact of the highly conserved proximal residue | ễFEBS Journal Probing the catalytic potential of the hamster arylamine N-acetyltransferase 2 catalytic triad by site-directed mutagenesis of the proximal conserved residue Tyr190 Xin Zhou1 Naixia Zhang2 Li Liu1 Kylie J. Walters2 Patrick E. Hanna1 and Carston R. Wagner1 1 Department of MedicinalChemistry University of Minnesota Minneapolis MN USA 2 Department of Biochemistry Molecular Biology and Biophysics University of Minnesota Minneapolis MN USA Keywords arylamine carcinogen N-acetyltransferase NAT kinetics pKa Correspondence C. R. Wagner Department of Medicinal Chemistry University of Minnesota 8-174 Weaver Densford Hall 308 Harvard St. . Minneapolis MN 55455 USA Fax 1 612 624 0139 Tel 1 612 624 2614 E-mail wagne003@ Received 14 July 2009 revised 3 September 2009 accepted 17 September 2009 doi Arylamine N-acetyltransferases NATs play an important role in both the detoxification of arylamine and hydrazine drugs and the activation of arylamine carcinogens. Because the catalytic triad Cys-His-Asp of mammalian NATs has been shown to be essential for maintaining protein stability rendering it impossible to assess alterations of the triad on catalysis we explored the impact of the highly conserved proximal residue Tyr190 which forms a direct hydrogen bond interaction with one of the triad residues Asp122 as well as a potential pi-pi stacking interaction with the active site His107. The replacement of hamster NAT2 Tyr190 by either Phe Ile or Ala was well tolerated and did not result in significant alterations in the overall fold of the protein. Nevertheless stopped-flow and steady-state kinetic analysis revealed that Tyr190 was critical for maximizing the acetylation rate of NAT2 and the transacetylation rate of p-amino-benzoic acid when compared with the wild-type. Tyr190 was also shown to play an important role in determining the pKa of the active site Cys during acetylation as well as the pH versus the rate profile for .

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