ROLE OF HISTIDINE RESIDUES IN THE CYCLODEXTRIN GLYCOSYLTRANSFERASE FROM Bacillus circulans DF 9R

COSTA, HERNÁN; DEL CANTO, SERGIO; FERRAROTTI, SUSANA; BISCOGLIO DE JIMÉNEZ BONINO, MIRTHA

Pinamar, Buenos Aires, Argentina

Congreso; X Congress of the Panamerican Association for Biochemistry and Molecular Biology (PABMB), XLI Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology (SAIB) and XX Annual Meeting of the Argentine Society for Neurochemistry; 2005

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Cyclodextrin glycosyltransferase (CGTase; EC 2.4.1.19) catalyses the conversion of starch and alpha(1-4) related glucans into cyclodextrins through intramolecular transglycosylation. The enzyme is also capable of catalysing starch hydrolysis and transglycosylation intermolecular reactions. Three histidine (His) residues are conserved in all CGTases described. Three-dimensional structure of CGTases from other sources has shown that such residues are located at or near the active site. Besides, it has been proposed that they are involved in the substrate binding site. On the other hand, protein reaction with diethyl pyrocarbonate (DEP) under mild conditions, leads to N-ethoxyformyl-derivatives. To search the role of His residues in functional aspects of the Bacillus circulans DF 9R CGTase, the effect of protein DEP-modification on hydrolytic and beta-cyclizing activities were measured. Results indicated that, with a DEP/His ratio of two, ethoxyformylation follows a pseudo first order kinetics and only one His residue is modified. This fact, leading to a drop of 75% in both activities, may be due to an alteration of the enzyme-substrate affinity.