STRUCTURAL STUDIES OF THE TRAPP MEMBRANE TETHERING COMPLEX

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 多聚体膜系留复合物TRAPPI和TRAPPII在囊泡到高尔基体的运输中起作用，在分泌囊泡到达高尔基体时以及在其融合以释放其货物之前起识别作用。 TRAPPI和TRAPPII共有七个亚基，其中四个（Bet 3 p，Bet 5 p，Trs 23 p和Trs 31 p）是激活Rab GT3 Ypt 1 p所需的最低限度，这是随后膜融合所需的事件。我们已经确定了一个杂五聚体TRAPP子组件的结构足以激活与Ypt 1 p复合。与Rab复合的多聚体系链组装的这一观点为在分子水平上理解膜融合之前的事件提供了框架。 基于该结构，我们提出TRAPPI通过稳定Ypt 1 p的核苷酸结合口袋来促进核苷酸交换，使其处于开放的、可接近的构象。其中三个亚基直接与Ypt 1 p相互作用以稳定这种形式，而一个亚基（Bet 3 p）的C-末端侵入核苷酸结合口袋并可能启动重塑。其中一个亚基（Trs 31 p）不直接与Ypt 1 p相互作用，而是变构调节TRAPP与Ypt 1 p的界面。TRAPPII可能通过与TRAPPI相同的机制激活Ypt 1 p。

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. The multimeric membrane-tethering complexes TRAPPI and TRAPPII function in vesicle traffic to the Golgi apparatus, playing a role in recognition as the secretory vesicle arrives at the Golgi and before it fuses to release its cargo. TRAPPI and TRAPPII share seven subunits, of which four (Bet3p, Bet5p, Trs23p, and Trs31p) are minimally required to activate the Rab GTPase Ypt1p, an event required for subsequent membrane fusion. We have determined the structure of a heteropentameric TRAPP subassembly sufficient for activation complexed with Ypt1p. This view of a multimeric tethering assembly in complex with a Rab provides a framework for understanding events preceding membrane fusion at a molecular level.. Based on the structure, we propose that TRAPPI promotes nucleotide exchange by stabilizing the nucleotide binding pocket of Ypt1p in an open, accessible conformation. Three of the subunits interact directly with Ypt1p to stabilize this form, while the C-terminus of one subunit (Bet3p) invades the nucleotide binding pocket and may initiate the remodeling. One of the subunits (Trs31p) does not interact directly with Ypt1p but allosterically regulates the TRAPP interface with Ypt1p. TRAPPII likely activates Ypt1p by the same mechanism as TRAPPI.