Moss J, Vaughan M
Pulmonary-Critical Care Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA.
Mol Cell Biochem. 1999 Mar;193(1-2):153-7.
ADP-ribosylation factors (ARFs) are members of a multigene family of 20-kDa guanine nucleotide-binding proteins that are regulatory components in several pathways of intracellular vesicular trafficking. The relatively small (approximately 180-amino acids) ARF proteins interact with a variety of molecules (in addition to GTP/GDP, of course). Cholera toxin was the first to be recognized, hence the name. Later it was shown that ARF also activates phospholipase D. Different parts of the molecule are responsible for activation of the two enzymes. In vesicular trafficking, ARF must interact with coatomer to recruit it to a membrane and thereby initiate vesicle budding. ARF function requires that it alternate between GTP- and GDP-bound forms, which involves interaction with regulatory proteins. Inactivation of ARF-GTP depends on a GTPase-activating protein or GAP. A guanine nucleotide-exchange protein or GEP accelerates release of bound GDP from inactive ARF-GDP to permit GTP binding. Inhibition of GEP by brefeldin A (BFA) blocks ARF activation and thereby vesicular transport. In cells, it causes apparent disintegration of Golgi structure. Both BFA-sensitive and insensitive GEPs are known. Sequences of peptides from a BFA-sensitive GEP purified in our laboratory revealed the presence of a Sec7 domain, a sequence of approximately 200 amino acids that resembles a region in the yeast Sec7 gene product, which is involved in Golgi vesicular transport. Other proteins of unknown function also contain Sec7 domains, among them a lymphocyte protein called cytohesin-1. To determine whether it had GEP activity, recombinant cytohesin-1 was synthesized in E. coli. It preferentially activated class I ARFs 1 and 3 and was not inhibited by BFA but failed to activate ARF5 (class II). There are now five Sec7 domain proteins known to have GEP activity toward class I ARFs. It remains to be determined whether there are other Sec7 domain proteins that are GEPs for ARFs 4, 5, or 6.
ADP核糖基化因子（ARFs）是一个由20 kDa鸟嘌呤核苷酸结合蛋白组成的多基因家族成员，是细胞内囊泡运输多种途径中的调节成分。相对较小（约180个氨基酸）的ARF蛋白与多种分子相互作用（当然，除了GTP/GDP之外）。霍乱毒素是第一个被识别的，因此得名。后来发现ARF还能激活磷脂酶D。分子的不同部分负责激活这两种酶。在囊泡运输中，ARF必须与包被蛋白相互作用，将其招募到膜上，从而启动囊泡出芽。ARF的功能要求它在结合GTP和GDP的形式之间交替，这涉及与调节蛋白的相互作用。ARF-GTP的失活取决于GTP酶激活蛋白或GAP。鸟嘌呤核苷酸交换蛋白或GEP加速从无活性的ARF-GDP中释放结合的GDP，以允许GTP结合。布雷菲德菌素A（BFA）对GEP的抑制作用会阻断ARF的激活，从而阻断囊泡运输。在细胞中，它会导致高尔基体结构明显解体。已知有对BFA敏感和不敏感的GEP。从我们实验室纯化的一种对BFA敏感的GEP的肽序列显示存在一个Sec7结构域，这是一个约200个氨基酸的序列，类似于酵母Sec7基因产物中的一个区域，该区域参与高尔基体囊泡运输。其他功能未知的蛋白质也含有Sec7结构域，其中包括一种名为细胞黏附分子-1的淋巴细胞蛋白。为了确定它是否具有GEP活性，在大肠杆菌中合成了重组细胞黏附分子-1。它优先激活I类ARFs 1和3，不受BFA抑制，但不能激活ARF5（II类）。现在已知有五种Sec7结构域蛋白对I类ARFs具有GEP活性。对于ARFs 4、5或6的其他Sec7结构域蛋白是否为GEP，仍有待确定。
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