Investigation on the Effects of Three X → Histidine Replacements on Thermostability of α-Amylase from Bacillus amyloliquefaciens
2012
Haghani, Karimeh, Tarbiat Modares University, Tehran, Iran | Khajeh, Khosro, Tarbiat Modares University, Tehran, Iran | Naderi-Manesh, Hossein, Tarbiat Modares University, Tehran, Iran | Ranjbar, Bijan, Tarbiat Modares University, Tehran, Iran
Bacillus licheniformis α-amylase (BLA), a thermophilic counterpart of Bacillus amyloliquefaciens α-amylase (BAA), is an appropriate model for the design of stabilizing mutations in BAA. BLA has 10 more histidines than BAA. Considering this prominent difference, in the present study, three out of these positions (I34, Q67, and P407; located in the thermostability determinant 1 region and Ca-Ⅲ binding site of BAA) were replaced with histidine in BAA, using the site-directed mutagenesis technique. The results showed that the thermostability of P407H and Q67H mutants had increased, but no significant changes were observed in their kinetic parameters compared to that of the wild type. I34H replacement resulted in complete loss of enzyme activity. Moreover, fluorescence and circular dichroism data indicated a more rigid structure for the P407H variant compared with that of the wild-type BAA. However, the flexibility of Q67H and I34H mutants increased in comparison with that of wild-type enzyme.
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