Organization, dynamics, and segregation of Ras nanoclusters in membrane domains
Organization, dynamics, and segregation of Ras nanoclusters in membrane domains
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DOI：
10.1073/pnas.1200773109
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发表时间：
2012-05-22
影响因子：
11.1
通讯作者：
Gorfe, Alemayehu A.
中科院分区：
文献类型：
--
作者：
Janosi, Lorant;Li, Zhenlong;Gorfe, Alemayehu A.
近期实验表明，膜结合的Ras蛋白形成瞬时的、纳米级的信号平台，在高保真信号传递中起关键作用。然而，通过高分辨率实验技术对这些动态的蛋白脂质亚结构进行详细表征仍然难以实现。在此，我们利用大量的半原子模拟来揭示Ras纳米簇形成和区域特异性分布的分子基础。作为模型系统，我们选择了H - ras的三重脂化膜靶向基序（tH）以及由二棕榈酰磷脂酰胆碱（DPPC）、二亚油酰磷脂酰胆碱（DLiPC）和胆固醇组成的大双层膜。我们发现4 - 10个tH分子组装成簇，其在亚微秒到微秒的时间尺度内发生分子交换，这取决于模拟温度以及脂质区域的稳定性。由于tH的棕榈酰基和法尼基对有序和无序膜区域的相反偏好，成簇的tH分子分离到脂质区域的边界。此外，对去棕榈酰化和去法尼基化的tH变体进行系统分析，使我们能够解读单个脂质修饰在区域特异性纳米簇定位中的作用，从而解释为什么同源的Ras异构体形成不重叠的纳米簇。而且，tH纳米簇在区域边界的定位导致线张力显著降低以及膜曲率增加。综上所述，这些结果为脂质修饰促进的蛋白质组装如何调节双层膜形状以产生功能性信号平台提供了独特的机制见解。
Recent experiments have shown that membrane-bound Ras proteins form transient, nanoscale signaling platforms that play a crucial role in high-fidelity signal transmission. However, a detailed characterization of these dynamic proteolipid substructures by high-resolution experimental techniques remains elusive. Here we use extensive semiatomic simulations to reveal the molecular basis for the formation and domain-specific distribution of Ras nanoclusters. As model systems, we chose the triply lipidated membrane targeting motif of H-ras (tH) and a large bilayer made up of di16: 0-PC (DPPC), di18:2-PC (DLiPC), and cholesterol. We found that 4-10 tH molecules assemble into clusters that undergo molecular exchange in the sub-mu s to mu s time scale, depending on the simulation temperature and hence the stability of lipid domains. Driven by the opposite preference of tH palmitoyls and farnesyl for ordered and disordered membrane domains, clustered tH molecules segregate to the boundary of lipid domains. Additionally, a systematic analysis of depalmitoylated and defarnesylated tH variants allowed us to decipher the role of individual lipid modifications in domain-specific nanocluster localization and thereby explain why homologous Ras isoforms form nonoverlapping nanoclusters. Moreover, the localization of tH nanoclusters at domain boundaries resulted in a significantly lower line tension and increased membrane curvature. Taken together, these results provide a unique mechanistic insight into how protein assembly promoted by lipid-modification modulates bilayer shape to generate functional signaling platforms.