STRUCTURAL STUDIES OF THE EXOCYST COMPLEX

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 RAB GTP酶是RAS样GTP酶超家族中最大的亚类，在细胞内小泡运输的多个步骤中发挥调节作用。它们被鸟嘌呤核苷酸交换因子(GEF)激活，后者催化GDP结合的或非活性的RAB形式向GTP结合的或活性形式的相互转化。对GEF激活RAB的机制知之甚少。在这里，我们介绍了Sec2p与其Rab伙伴Sec4p形成的络合物中SEC2p的GF域的晶体结构。Sec2p全球环境基金结构域是一个220A长的卷曲线圈，其简单和使用卷曲线圈的催化基序引人注目。该结构提示了一种机制，即Sec2p在Sec4p开关区和磷酸结合环中诱导与核苷酸结合不相容的广泛结构重排。我们发现Sec2p对Sec4p是特异的，特异性决定因素存在于Sec4p的两个开关区。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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 A 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.