Brandão R L, Castro I M, Bambirra E A, Amaral S C, Fietto L G, Tropia M J, Neves M J, Dos Santos R G, Gomes N C, Nicoli J R
Laboratório de Fisologia e Bioquímica de Microorganismos, Escola de Farmácia, Universidade Federal de Ouro Preto, Brazil.
Appl Environ Microbiol. 1998 Feb;64(2):564-8. doi: 10.1128/AEM.64.2.564-568.1998.
As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S.cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.
如同布拉氏酵母菌的情况一样，酿酒酵母W303可保护费希尔大鼠免受霍乱毒素（CT）的侵害。向在非发酵碳源上生长的布拉氏酵母菌细胞中添加葡萄糖或二硝基苯酚，会以与酿酒酵母中观察到的方式类似的方式激活海藻糖酶。向相同细胞中添加CT也会导致海藻糖酶激活。分别对CT的A亚基和B亚基进行的实验表明，两者对于激活都是必需的。同样，添加CT而非其单独的亚基会在布拉氏酵母菌和酿酒酵母中均产生环磷酸腺苷（cAMP）信号。这些数据表明，CT对海藻糖酶的刺激可能是通过cAMP介导的蛋白质磷酸化级联反应发生的。CT亚基B对cAMP信号和海藻糖酶激活均有需求，这表明酵母上存在能够结合该毒素的特异性受体，这种情况与在哺乳动物细胞中观察到的情况类似。用125I标记的CT进行的实验显示该毒素与酵母细胞的特异性结合，则强化了这一假设。CT通过B亚基与酵母表面的受体结合以及A亚基的内化（这对于cAMP信号和海藻糖酶激活是必需的）可能是另一种机制，可解释在用酵母处理的大鼠中观察到的对该毒素的保护作用。
