Noda M, Tsai S C, Adamik R, Moss J, Vaughan M
Laboratory of Cellular Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
Biochim Biophys Acta. 1990 May 16;1034(2):195-9. doi: 10.1016/0304-4165(90)90076-9.
Cholera toxin causes the devastating diarrheal syndrome characteristic of cholera by catalyzing the ADP-ribosylation of Gs alpha, a GTP-binding regulatory protein, resulting in activation of adenylyl cyclase. ADP-ribosylation of Gs alpha is enhanced by 19 kDa guanine nucleotide-binding proteins known as ADP-ribosylation factors or ARFs. We investigated the effects of agents known to alter toxin-catalyzed activation of adenylyl cyclase on the stimulation of toxin- and toxin subunit-catalyzed ADP-ribosylation of Gs alpha and other substrates by an ADP-ribosylation factor purified from a soluble fraction of bovine brain (sARF II). In the presence of GTP, sARF II enhanced activity of both the toxin catalytic unit and a reduced and alkylated fragment ('A1'), as a result of an increase in substrate affinity with no significant effects on Vmax. Activation of toxin was independent of Gs alpha and was stimulated 4-fold by sodium dodecyl sulfate, but abolished by Triton X-100. sARF II therefore serves as a direct allosteric activator of the A1 protein and may thus amplify the pathological effects of cholera toxin.
霍乱毒素通过催化Gsα（一种GTP结合调节蛋白）的ADP核糖基化，导致腺苷酸环化酶激活，从而引发霍乱特有的严重腹泻综合征。19 kDa的鸟嘌呤核苷酸结合蛋白（称为ADP核糖基化因子或ARFs）可增强Gsα的ADP核糖基化。我们研究了已知能改变毒素催化的腺苷酸环化酶激活的试剂对从牛脑可溶性部分纯化的ADP核糖基化因子（sARF II）刺激毒素和毒素亚基催化的Gsα及其他底物的ADP核糖基化的影响。在GTP存在的情况下，sARF II增强了毒素催化单元和还原烷基化片段（“A1”）的活性，这是由于底物亲和力增加，而对Vmax没有显著影响。毒素的激活不依赖于Gsα，十二烷基硫酸钠可使其激活增强4倍，但Triton X - 100可将其激活作用消除。因此，sARF II作为A1蛋白的直接变构激活剂，可能会放大霍乱毒素的病理效应。
