Mechanisms of Membrane Fusion

膜融合是荷尔蒙分泌、神经传递和所有胞外和 内吞流量。它的机制从酵母到人类都是保守的。当前的范例 表明被称为SNARs的膜蛋白在锚定时不可阻挡地推动融合 相反的膜作为反式SNARE复合体。虽然诱捕是必需的，但基因研究 从酵母到人类的研究表明，Rab GTP酶、其效应器、SM蛋白和SNARE 监护人也是必不可少的。我们对酵母液泡融合的研究为我们提供了一种新的 范例，阐明了这些其他基本蛋白质的整合机制，并展示了 他们的行动超越了对跨圈套复杂级别的监管。液泡融合 研究已经从最初的遗传学发展到我们对体外细胞器的广泛研究。 融合到蛋白脂质体融合，我们已经用所有纯化和定义的 蛋白质和脂类：圈套、圈套分解伴侣Sec18p/Sec17p、Rab GTPase Ypt7p，一种六聚体Rab效应器复合体HOP，以及包括酸性和 反对双层的头基和特定的脂肪酰链。通过严格的融合分析 受保护的管腔内容物混合，我们的研究表明融合是由几个合作推动的 影响因素：跨SNARE复合体的双层应力，膜的不稳定性 非双层脂类，以及通过多亚单位系绳作用而发生的双层弯曲。核聚变是 被圈套、非双层倾向脂类或系留因子的遗漏所阻断，甚至 尽管在后两种情况下，陷阱仍然在反式中配对。我们的化学定义的重组 融合允许圈套浓度、非双分子层脂质浓度、 以及啤酒花和Rab系留蛋白，所有这些都是在分析物理关联和 融合功能。测试和扩展这一模型系统正在改变我们对融合的看法。在灯光下 融合在整个人类生理学中的基础作用，以及人类的中心作用 用于马尔堡和埃博拉病毒以及病原体等细菌的细胞感染的啤酒花 伯氏柯克斯体，这些研究也将具有医学意义。

Membrane fusion underlies hormone secretion, neurotransmission, and all exocytic and endocytic traffic. Its mechanism is conserved from yeast to humans. A current paradigm suggests that membrane proteins termed SNAREs inexorably drive fusion when anchored in apposed membranes as a trans-SNARE complex. While SNAREs are required, genetic studies from yeast to humans show that Rab GTPases, their effectors, SM proteins, and SNARE chaperones are also essential. Our studies of yeast vacuole fusion are providing a new paradigm, illuminating the integrated mechanisms of these other essential proteins and showing that their actions extend beyond regulation of trans-SNARE complex levels. Vacuole fusion studies have progressed from initial genetics through our extensive study of in vitro organelle fusion to proteoliposome fusion, which we have reconstituted with all purified and defined proteins and lipids: SNAREs, SNARE disassembly chaperones Sec18p/Sec17p, the Rab GTPase Ypt7p, a hexameric Rab effector complex HOPS, and lipids which include acidic and bilayer-averse headgroups and specific fatty acyl chains. With a rigorous fusion assay of protected lumenal content mixing, our studies show that fusion is driven by several cooperating factors: bilayer stress from trans-SNARE complex assembly, membrane destabilization by nonbilayer lipids, and bilayer bending through the action of a multisubunit tether. Fusion is blocked by the omission of SNAREs, of nonbilayer-prone lipids, or of tethering factors, even though SNAREs still pair in trans in the latter 2 conditions. Our chemically-defined reconstitution of fusion allows independent variation of SNARE concentration, nonbilayer lipid concentration, and the HOPS and Rab tethering proteins, all while assaying both physical associations and fusion function. Testing and extending this model system is changing our view of fusion. In light of the fundamental role of fusion throughout human physiology, and the central role of human HOPS for cellular infection by Marburg and Ebola viruses and by bacteria such as the pathogen Coxiella burnetii, these studies will be of medical significance as well.