Jeang Chii-Ling, Lin Da-Gin, Hsieh Shu-Hui
Department of Food Science, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan, Republic of China.
J Agric Food Chem. 2005 Aug 10;53(16):6301-4. doi: 10.1021/jf0503356.
The plasmid pHG contains a cyclodextrin glycosyltransferase (CGTase) gene (cgt) derived from Bacillus macerans. Two transformants, Bacillus subtilis (pHG) and Escherichia coli (pHG), were found to produce CGTases with the same primary structure as the enzyme from B. macerans. However, the beta-cyclodextrin coupling activity of the CGTase from E. coli (pHG) was 14-fold higher than that of the enzymes from the other strains. By contrast, no differences in alpha-cyclodextrin coupling activities were observed among these CGTases. CGTase from E. coli (pHG) was found to be less thermostable than the other CGTases. When the CGTase produced by B. subtilis was treated with increasing urea concentrations (10-1000 mM) to promote increasing degrees of protein unfolding, a bell-shaped beta-cyclodextrin coupling activity profile was obtained. Subtle differences in the conformation of the CGTase produced by E. coli are therefore proposed to be responsible for the markedly increased beta-cyclodextrin coupling activity of this enzyme.
质粒pHG含有一个来源于浸麻芽孢杆菌的环糊精糖基转移酶（CGTase）基因（cgt）。发现两株转化体，枯草芽孢杆菌（pHG）和大肠杆菌（pHG），能够产生与浸麻芽孢杆菌的酶具有相同一级结构的CGTases。然而，大肠杆菌（pHG）的CGTase的β-环糊精偶联活性比其他菌株的酶高14倍。相比之下，这些CGTases之间未观察到α-环糊精偶联活性的差异。发现大肠杆菌（pHG）的CGTase比其他CGTases热稳定性更低。当用浓度不断增加的尿素（10 - 1000 mM）处理枯草芽孢杆菌产生的CGTase以促进蛋白质展开程度增加时，获得了一个钟形的β-环糊精偶联活性曲线。因此，有人提出大肠杆菌产生的CGTase构象的细微差异是该酶β-环糊精偶联活性显著增加的原因。
