Araki S, Kikuchi A, Hata Y, Isomura M, Takai Y
Department of Biochemistry, Kobe University School of Medicine, Japan.
J Biol Chem. 1990 Aug 5;265(22):13007-15.
We have previously purified from bovine brain cytosol a novel regulatory protein for smg p25A, a ras p21-like GTP-binding protein. This protein, named smg p25A GDP dissociation inhibitor (GDI), regulates the GDP/GTP exchange reaction of smg p25A by inhibiting the dissociation of GDP from and thereby the subsequent binding of GTP to it. We have also previously found that smg p25A is mainly localized in presynaptic plasma membranes and vesicles and moderately in presynaptic cytosol in rat brain synapses. In this paper, we have studied the possible involvement of smg p25A GDI in the localization of smg p25A in the cytosol, plasma membranes, and vesicles in rat brain synapses. Both the GDP- and GTP-bound forms of smg p25A bound to the synaptic membranes and vesicles. smg p25A GDI inhibited the binding of the GDP-bound form of smg p25A, but not that of the GTP-bound form, to the synaptic membranes and vesicles. Moreover, smg p25A GDI induced the dissociation of the GDP-bound form, but not that of the GTP-bound form, of both endogenous and exogenous smg p25As from the synaptic membranes and vesicles. smg p25A GDI made a complex with the GDP-bound form of smg p25A with a molar ratio of 1:1, but not with the GTP-bound or guanine nucleotide-free form. These results suggest that smg p25A reversibly binds to synaptic plasma membranes and vesicles and that this reversible binding is regulated by its specific GDI.
我们之前已从牛脑细胞质中纯化出一种针对smg p25A的新型调节蛋白，smg p25A是一种类Ras p21的GTP结合蛋白。这种名为smg p25A GDP解离抑制剂（GDI）的蛋白，通过抑制GDP从smg p25A上解离，进而抑制随后GTP与之结合，来调节smg p25A的GDP / GTP交换反应。我们之前还发现，smg p25A主要定位于大鼠脑突触的突触前质膜和囊泡中，在突触前细胞质中含量适中。在本文中，我们研究了smg p25A GDI在大鼠脑突触的细胞质、质膜和囊泡中smg p25A定位过程中可能发挥的作用。smg p25A的GDP结合形式和GTP结合形式均能与突触膜和囊泡结合。smg p25A GDI抑制了smg p25A的GDP结合形式与突触膜和囊泡的结合，但不抑制GTP结合形式的结合。此外，smg p25A GDI诱导内源性和外源性smg p25A的GDP结合形式从突触膜和囊泡上解离，但不诱导GTP结合形式的解离。smg p25A GDI与smg p25A的GDP结合形式以1:1的摩尔比形成复合物，但不与GTP结合形式或无鸟嘌呤核苷酸形式形成复合物。这些结果表明，smg p25A与突触质膜和囊泡可逆性结合，且这种可逆性结合受其特异性GDI的调节。
