Sunday, July 29, 2007
P11
Site-directed mutagenesis of calcium-binding S231 residue in naringin specific β-cyclodextrin glucanotransferase for thermostability
Yong-Hyun Lee, Young-Hoon Go, Kwang-Woo Lee, and Tae-Kwon Kim. Department of Genetic Engineering, Kyungpook National University, Daegu, South Korea
A serine residue at position 231 in β-cyclodextrin glucanotransferase (β-CGTase) from alkalophilic Bacillus sp. BL-31 highly specific for bioflavonoid naringin was modified by site-directed mutagenesis to improve the thermostability. The thermostability of a mutant β-CGTase replaced with S231D increased the thermostability remarkably up to 4.2-fold compared to the wild-type at 50°C. The half-life of S231D mutant enzyme at 50°C increased from 20 min to 2 h. The intermolecular transglycosylation was carried out using S231D mutant β-CGTase at a high temperature of 60°C to enhance the solubility of immiscible naringin for 6 h, and a high conversion yield as high as 80% was achieved compared to 19% of wild-type even at an extremely high naringin concentration of 50 g/l.
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