Allende J E
Department of Biochemistry, Faculty of Medicine, University of Chile, Santiago.
FASEB J. 1988 May;2(8):2356-67. doi: 10.1096/fasebj.2.8.2452111.
G proteins that serve to transduce external signals in membranes share with protein synthesis factors and tubulin structural and functional features that are common to proteins that participate in reversible GTP-mediated macromolecular interactions. These proteins can bind GTP and GDP with high affinity, adopting different structures depending on whether they are complexed with the nucleotide diphosphate or triphosphate. The GTP.protein complex has high affinity for an acceptor macromolecule (or complex of macromolecules) and interacts with it, affecting its activity. These GTP-binding proteins also possess an intrinsic GTPase activity that is generally stimulated by its interaction with the acceptor. The GTPase activity converts the bound GTP to GDP, switching the configuration of the complexed protein to one of low affinity for the acceptor and causing its dissociation. The protein.GDP complex must exchange its GDP for GTP to allow the protein to acquire the high-affinity structure that can cycle back to the acceptor macromolecule. This exchange of guanine nucleotides requires in several instances exchange factors that can regulate the whole process. A detailed comparison of the features of the different systems is made with respect to structural similarities, regulation by protein phosphorylation, ADP ribosylation by bacterial toxins, and requirements for exchange factors. It is also proposed that there is a similar mechanism that involves ATP/ADP-binding proteins.
在膜中用于转导外部信号的G蛋白与蛋白质合成因子和微管蛋白具有结构和功能特征，这些特征对于参与可逆GTP介导的大分子相互作用的蛋白质而言是共同的。这些蛋白质能够以高亲和力结合GTP和GDP，根据它们是与二磷酸核苷酸还是三磷酸核苷酸复合而呈现不同的结构。GTP - 蛋白质复合物对受体大分子（或大分子复合物）具有高亲和力，并与之相互作用，影响其活性。这些GTP结合蛋白还具有内在的GTP酶活性，通常通过其与受体的相互作用而被激活。GTP酶活性将结合的GTP转化为GDP，将复合蛋白的构象转变为对受体低亲和力的构象之一，并导致其解离。蛋白质 - GDP复合物必须将其GDP交换为GTP，以使蛋白质获得能够循环回到受体大分子的高亲和力结构。这种鸟嘌呤核苷酸的交换在几种情况下需要能够调节整个过程的交换因子。针对结构相似性、蛋白质磷酸化调节、细菌毒素的ADP核糖基化以及对交换因子的需求，对不同系统的特征进行了详细比较。还提出存在一种涉及ATP / ADP结合蛋白的类似机制。
