Membrane-Transport Signaling Involving the GTPase Cycle of G proteins

G蛋白在GTP-和gdp结合状态的两种不同构象之间循环，在许多细胞内信号通路中作为“分子开关”发挥重要作用。G蛋白家族包括1)参与蛋白质合成和mRNA降解的翻译因子，2)三聚体G蛋白，以及3)小gtp酶。小的gtp酶，如Ras、Rab、Arf和Rho/Rac家族，参与调节细胞生长和分化、细胞内囊泡运输、细胞形状和粘附。然而，仍有许多其他小的gtp酶，其功能尚不清楚。在这项研究中，我们已经鉴定和表征了具有独特生化特性或组织表达的新型小gtpase。在线虫巨噬细胞样体腔细胞中，ar18 GTPase对溶酶体的生物生成至关重要：ARL-8主要定位于溶酶体，ARL-8的缺失突变体显示出小尺寸和非a - 1的溶酶体数量增加。胞外大分子在arl-8突变体中被内吞并通过内体运输，但其降解明显减少。因此，ar18似乎是溶酶体生物发生/功能的重要调节因子。Rab45是一个非典型的GTPase，在中间区域包含一个卷曲的螺旋基序和一个独特的n端EF-hand结构域和c端rab -同源结构域。Rab45具有自相互作用能力，而自相互作用需要含有线圈基序的中间区域。在HeLa细胞中表达的Rab45定位于细胞核周的一小块区域，其定位受Rab45的鸟嘌呤核苷酸结合状态的调控。中间区域和Rab结构域似乎对Rab45.3的核周定位至关重要。Di-Ras属于Ras家族的一个独特分支，主要以gtp结合形式存在于活细胞中。Di-Ras在神经元细胞中的表达具有特异性，其过表达可诱导神经元细胞凋亡并发生DNA断裂。秀丽隐杆线虫arl-8缺失突变体表现出神经细胞乙酰胆碱释放可能受损的表型。少

G proteins, which cycle between the two different conformations of GTP- and GDP-bound states, play important roles as a "molecular switch" in many intracellular signaling pathways. The G protein families include 1) translation factors involved in protein synthesis and mRNA degradation, 2) trimeric G proteins, and 3) small GTPases. The small GTPases, such as Ras, Rab, Arf, and Rho/Rac family, are involved in the regulation of cell growth and differentiation, intracellular vesicle trafficking, and cell shape and adhesion. However, there are still many other small GTPases, of which functions are unknown. In this study, we have identified and characterized novel small GTPases exhibiting unique biochemical properties or tissue expression.1. The Arl8 GTPase was essential for lysosome biogenesis in the macrophage-like coelomocytes of C. elegans: ARL-8 localized primarily to lysosomes, and a deletion mutant of arl-8 displayed an increase in number of lysosomes that were small in size and non-a … More cidic. Extracellular macromolecules were endocytosed and transported through endosomes in arl-8 mutant coelomocytes, but its degradation was markedly reduced. Thus, Arl8 appeared to function as an important regulator of lysosome biogenesis/function.2. Rab45 is an atypical GTPase that contains a coiled-coil motif at the mid region and a distinct N-terminal EF-hand domain with C-terminal Rab-homology domain. Rab45 was capable of self-interacting, and the self-interaction required the mid region containing the coiled-coil motif. Rab45 expressed in HeLa cells was localized in a small patch in the perinuclear area of the cell, and the localization was regulated by the guanine nucleotide-bound states of Rab45. The mid region, together with Rab domain, appeared to be essential for the characteristic perinuclear localization of Rab45.3. Di-Ras, which belongs to a distinct branch of the Ras family, existed predominantly as a GTP-bound form in living cells. The expression of Di-Ras was rather specific in neuronal cells, and its over-expression induced apoptotic cell death with DNA fragmentation in neuronal cells. A deletion mutant of arl-8 in C. elegans displayed a phenotype that acetylcholine release from nerve cells might be impaired. Less