Dong Gang, Medkova Martina, Novick Peter, Reinisch Karin M
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
Mol Cell. 2007 Feb 9;25(3):455-62. doi: 10.1016/j.molcel.2007.01.013.
Rab GTPases, the largest subgroup in the superfamily of Ras-like GTPases, play regulatory roles in multiple steps of intracellular vesicle trafficking. They are activated by guanine nucleotide exchange factors (GEFs), which catalyze the interconversion of the GDP-bound, or inactive, form of Rab to the GTP-bound, or active, form. Relatively little is known of the mechanisms by which GEFs activate Rabs. Here, we present the crystal structure of the GEF domain of Sec2p in complex with its Rab partner Sec4p. The Sec2p GEF domain is a 220 Angstroms long coiled coil, striking in its simplicity and in the use of the coiled-coil motif for catalysis. The structure suggests a mechanism whereby Sec2p induces extensive structural rearrangements in the Sec4p switch regions and phosphate-binding loop that are incompatible with nucleotide binding. We show that Sec2p is specific for Sec4p and that specificity determinants reside in the two switch regions of Sec4p.
Rab鸟苷三磷酸酶（GTPases）是类Ras鸟苷三磷酸酶超家族中最大的亚群，在细胞内囊泡运输的多个步骤中发挥调节作用。它们由鸟嘌呤核苷酸交换因子（GEFs）激活，这些因子催化Rab从结合GDP的非活性形式向结合GTP的活性形式的相互转化。关于GEFs激活Rab的机制，人们了解相对较少。在这里，我们展示了Sec2p的GEF结构域与其Rab伴侣Sec4p形成复合物的晶体结构。Sec2p的GEF结构域是一个220埃长的卷曲螺旋结构，其简单性以及利用卷曲螺旋基序进行催化的方式令人瞩目。该结构提示了一种机制，即Sec2p诱导Sec4p开关区域和磷酸结合环发生广泛的结构重排，这些重排与核苷酸结合不相容。我们表明Sec2p对Sec4p具有特异性，且特异性决定因素存在于Sec4p的两个开关区域。
