Two conserved amino acid residues in the extra sugar-binding space near the catalytic site of Thermus maltogenic amylase (ThMA) were analyzed for their role in the hydrolysis and transglycosylation activity of the enzyme. Site-directed mutagenesis was carried out by replacing N331 with a lysine (N331K), E332 with a histidine (E332H), or by replacing both residues at the same time (N331K/E332H). The measured Km values indicated that affinities toward all substrates tested, including starch, pullulan, β-cyclomaltodextrin, and acarbose, were lower in all the mutants compared to that of wild-type ThMA, leading to reduced hydrolysis activity. In addition, the lower ratio of transglycosylation to hydrolysis in the mutants compared to that in the wild-type ThMA indicated that these mutants preferred hydrolysis to the transglycosylation reaction. These results demonstrated that the conserved dipeptide at 331 and 332 of ThMA is directly involved in the formation and accumulation of transfer products by accommodating acceptor sugar molecules.
|Number of pages||7|
|Journal||Journal of Microbiology and Biotechnology|
|Publication status||Published - 2003 Dec 1|
- Site-directed mutagenesis
- Thermus maltogenic amylase (ThMA)
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology