The Mechanism of Membrane Fusion and Lipid Flip/Flop Explored with Model Transmembrane Helices

多种生物过程，如膜融合和跨膜脂类翻转/翻转，都是基于蛋白质/脂类的相互作用。在之前的工作中，我们已经开发了跨膜螺旋的低复杂性模型-LV-肽。这些多肽催化膜融合和脂类翻转。这些功能性质取决于螺旋的骨架动力学和侧翼残基的电荷状态。在这个提议中，我们提出了关于功能性质和结构性质如何联系的可测试假设。我们将使用互补的实验方法和模拟来检验这些假说，以阐明膜融合和脂类翻转的机制。特别是，我们将检查一系列LV-螺旋与化学上不同的脂类相互作用的能力。首先，这些TMD/脂质相互作用可以导致脂质扩散，从而启动膜融合。其次，我们将评估这些相互作用的共价稳定是否有助于脂质翻转，这将支持PC脂类在无序的膜域中翻转的想法。第三，我们将测试一个新的概念，其中PE脂类的翻转是通过TM螺旋和脂类的耦合膜转位来实现的。

A diversity of biological processes, like membrane fusion and lipid flip/flop across membranes, are based on protein/lipid interactions. In previous work, we have developed low-complexity models - the LV-peptides - of transmembrane helices. These peptides catalyze membrane fusion and lipid flip. These functional properties depend on the backbone dynamics of the helices and the charge state of the flanking residues. In this proposal, we present testable hypotheses as to how the functional and the structural properties could be connected. We will examine these hypotheses using complementary experimental approaches and simulations in order to clarify the mechanism of membrane fusion and lipid flip. In particular, we will examine the capacity of a range of LV-helices to interact with chemically distinct lipids. First, these TMD/lipid interaction could cause lipid splay and thereby initiate membrane fusion. Second, we will assess whether the covalent stabilization of these interactions facilitates lipid flip, which would support the idea that PC lipids flip within disordered membrane domains. Third, we will test a new concept where flip of PE lipids is enabled by a coupled membrane translocation of TM helix and lipids.