Studies on the conformation and functions of ras-related low Mr GTP-binding proteins.

众所周知，从酵母到哺乳动物都存在多种与ras相关的低MR GTP结合蛋白。我们已经纯化并鉴定了哺乳动物组织中的几种低MR GTP结合蛋白，如RhoA、Rac、Ram和C25KG蛋白。RhoA是人血小板中肉毒杆菌C3酶的唯一底物，可能参与细胞骨架的调节。我们观察到C3类酶存在于牛脑中，并对其进行了部分纯化。Rho蛋白也被观察到参与了平滑肌的收缩，尽管其机制尚未完全阐明。据报道，Rac蛋白在吞噬细胞中控制产生超氧化物的NADPH氧化酶系统，该系统由至少一个膜和三个胞浆成分组成。在酵母中，SAR1在细胞内蛋白运输中起着重要的作用，而RSR1与哺乳动物的同源物RAP1具有相似的功能。最近，人们报道了几种调节低MR GTP结合蛋白的蛋白。首次纯化、鉴定和克隆了ras p21的GTP酶激活蛋白(ras-GAP)。此后，我们纯化了SMG p21和Rho p20的GAP。GDP解离刺激物(GDS)和GDP解离抑制物(GDI)也被纯化并鉴定为一些低MR GTP结合蛋白，如ras p21、SMG蛋白、Rho p20和SMG p25A。研究了这些调节蛋白对GTP结合蛋白的作用方式，结果表明C-末端的预烯基化如法尼化和香叶基香叶化是其功能所必需的。

It is well known that a variety of ras-related low Mr GTP-binding proteins are present from yeast to mammalian. We have purified and identified several kinds of low Mr GTP-binding proteins such as rhoA, rac,ram and c25KG proteins in mammalian tissues. rhoA was identified a sole substrate of botulinum C3 enzyme in human platelet and suggested to be involved in cytoskeletal regulation. We observed that the C3 enzyme-like enzyme is present in bovine brain and partially purified it. rho protein was also observed to take part in contraction of smooth muscle although the mechanism has not been totally elucidated. rac protein was reported in phagocytes to control the superoxide-generating NADPH oxidase system which consists of at least one membrane and three cytosolic components. In yeast, SAR1 plays an essential role in intracellular protein transport and RSR1 has similar function as that of mammalian homolog, rap1.Recently, several kinds of regulatory proteins for low Mr GTP-binding proteins have been reported. GTPase activating protein for ras p21 (ras-GAP) was first purified, identified and cloned. Thereafter, we purified GAPs for smg p21 and rho p20. GDP dissociation stimulator (GDS) and GDP dissociation inhibitor (GDI) have also been purified and identified for some low Mr GTP-bining proteins such as ras p21, smg proteins, rho p20, and smg p25A. The modes of the action of these regulatory proteins on the GTP-binding proteins were investigated and it was shown that the C-terminal prenylation such as farnesylation and geranylgeranylation is necessary for their functions.