Department of Cell Biology, School of Medicine, Yale University, New Haven, Connecticut, USA.
Nat Struct Mol Biol. 2011 Jul 24;18(8):941-6. doi: 10.1038/nsmb.2102.
The core mechanism of intracellular vesicle fusion consists of SNAREpin zippering between vesicular and target membranes. Recent studies indicate that the same SNARE-binding protein, complexin (CPX), can act either as a facilitator or as an inhibitor of membrane fusion, constituting a controversial dilemma. Here we take energetic measurements with the surface force apparatus that reveal that CPX acts sequentially on assembling SNAREpins, first facilitating zippering by nearly doubling the distance at which v- and t-SNAREs can engage and then clamping them into a half-zippered fusion-incompetent state. Specifically, we find that the central helix of CPX allows SNAREs to form this intermediate energetic state at 9-15 nm but not when the bilayers are closer than 9 nm. Stabilizing the activated-clamped state at separations of less than 9 nm requires the accessory helix of CPX, which prevents membrane-proximal assembly of SNAREpins.
细胞内囊泡融合的核心机制包括囊泡和靶膜之间 SNAREpin 的拉链式连接。最近的研究表明，相同的 SNARE 结合蛋白复合蛋白 (CPX) 可以作为膜融合的促进剂或抑制剂发挥作用，构成了一个有争议的两难境地。在这里，我们使用表面力仪器进行能量测量，揭示 CPX 依次作用于组装的 SNAREpins，首先通过将 v-SNARE 和 t-SNARE 可以结合的距离几乎增加一倍来促进拉链式连接，然后将它们夹入半拉链式融合失活状态。具体来说，我们发现 CPX 的中心螺旋允许 SNARE 形成这种中间能量状态，距离为 9-15nm，但当双层膜距离小于 9nm 时则不能。将激活夹状态稳定在小于 9nm 的分离距离需要 CPX 的辅助螺旋，该螺旋防止 SNAREpins 在膜附近组装。
