The residue 179 is involved in product specificity of the Bacillus circulans DF 9R Cyclodextrin glycosyltransferase

COSTA, HERNÁN; DISTÉFANO, ANA JULIA; MARINO-BUSLJE, CRISTINA; HIDALGO, AURELIO; BERENGUER, CARLOS; BISCOGLIO DE JIMÉNEZ BONINO, MIRTHA; FERRAROTTI, SUSANA ALICIA

APPLIED MICROBIOLOGY AND BIOTECHNOLOGY

SPRINGER

Año: 2011 vol. 94 p. 123 - 130

0175-7598

Cyclodextrin glycosyltransferases (CGTases) are important enzymes in biotechnology because of their ability to produce cyclodextrin (CD) mixtures from starch whose relative composition depends on enzyme source. A multiple alignment of 46 CGTases and Shannon entropy analysis allowed us to find differences and similarities that could be related to product specificity. Interestingly, position 179 has Gly in all the CGTases except in that from Bacillus circulans DF 9R which possesses Gln. The absence of a side chain at that position has been considered as a strong requirement for substrate binding and cyclization process. Therefore, we constructed two mutants of this enzyme, Q179L and Q179G. The activity and kinetic parameters of Q179G remained unchanged while the Q179L mutant showed a different CDs ratio, a lower catalytic efficiency and a decreased ability to convert starch into CDs. We postulate that residue 179 is also involved in CGTases product specificity and cyclization reaction and, in the case of that from B. circulans DF 9R, Gln can interact with the sixth glucose ring of starch by establishing a hydrogen bond through a water molecule; these findings are also explained on the basis of a structural model.