title: Characterization of the active site thiol group of rhinovirus 2A proteinase.
abstract: Picornains 2A are cysteine proteases of picornaviruses, a virus family containing several human and animal pathogens. The pH dependencies of the alkylations of picornain 2A of rhinovirus type 2 with iodoacetamide and iodoacetate show two reactive thiol forms, namely the free thiolate ion at high pH and an imidazole assisted thiol group at low pH. Kinetic deuterium isotope effects do not support general base catalysis by the imidazole group, but rather the existence of a catalytically competent thiolate-imidazolium ion-pair. The nature of the ion-pair differs from that of papain, the paradigm of cysteine proteases. The ion-pair is confined to the same, unusually narrow pH range in which the enzyme exhibits catalytic activity.
authors.affiliation: Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, PO Box 7, Budapest H-1518, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Sárkány
authors.forename: T
authors.initials: T
authors.lastname: Skern
authors.forename: L
authors.initials: L
authors.lastname: Polgár
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D017666:Deuterium Oxide; D004228:Dithionitrobenzoic Acid / Q000737:chemistry; D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009842:Oligopeptides / Q000737:chemistry; D010084:Oxidation-Reduction; D012229:Rhinovirus / Q000201:enzymology*; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000737:chemistry; D017186:Titrimetry; D014764:Viral Proteins
chemical_list: D009842:Oligopeptides; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D014764:Viral Proteins; D004228:Dithionitrobenzoic Acid; D003546:Cysteine Endopeptidases; C057400:picornain 2A, Picornavirus; D017666:Deuterium Oxide