TAILIEUCHUNG - Báo cáo khoa học: The catalytic role of the distal site asparagine-histidine couple in catalase-peroxidases

Catalase-peroxidases (KatGs) are unique in exhibiting an overwhelming catalase activity and a peroxidase activity of broad specificity. Similar to other peroxidases the distal histidine inKatGs forms a hydrogen bond with an adjacent conserved asparagine. To investigate the catalytic role(s) of this potential hydrogen bond in the bifunctional activity of KatGs, Asn153 inSynechocystisKatG was replaced with either Ala (Asn153fiAla) or Asp (Asn153fiAsp). | Eur. J. Biochem. 270 1006-1013 2003 FEBS 2003 doi The catalytic role of the distal site asparagine-histidine couple in catalase-peroxidases Christa Jakopitsch1 Markus Auer1 Giinther Regelsberger1 Walter Jantschko1 Paul G. Furtmuller1 Florian Ruker2 and Christian Obinger1 1 Institute of Chemistry and 2Institute of Applied Microbiology University of Agricultural Sciences Vienna Austria Catalase-peroxidases KatGs are unique in exhibiting an overwhelming catalase activity and a peroxidase activity of broad specificity. Similar to other peroxidases the distal histidine in KatGs forms a hydrogen bond with an adjacent conserved asparagine. To investigate the catalytic role s of this potential hydrogen bond in the bifunctional activity of KatGs Asn153 in Synechocystis KatG was replaced with either Ala Asn153fiAla or Asp Asn153fiAsp . Both variants exhibit an overall peroxidase activity similar with wild-type KatG. Cyanide binding is monophasic however the second-order binding rates are reduced to Asn153fiAla and Asn153fiAsp of the value of native KatG X 105 M 1-s 1 at pH 7 and 15 C . The turnover number of catalase activity of Asn153fiAla is 6 and that of Asn153fiAsp is of wild-type activity. Stopped-flow analysis of the reaction of the ferric forms with H2O2 suggest that exchange of Asn did not shift significantly the ratio of rates of H2O2-mediated compound I formation and reduction. Both rates seem to be reduced most probably because a the lower basicity of His123 hampers its function as acid-base catalyst and b Asn153 is part of an extended KatG-typical H-bond network the integrity of which seems to be essential to provide optimal conditions for binding and oxidation of the second H2O2 molecule necessary in the catalase reaction. Keywords catalase-peroxidase Synechocystis PCC 6803 catalase activity peroxidase activity compound I. On the basis of sequence similarities with yeast cytochrome c peroxidase CCP and plant

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