Köster Darius Vasco, Husain Kabir, Iljazi Elda, Bhat Abrar, Bieling Peter, Mullins R Dyche, Rao Madan, Mayor Satyajit
National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India;
Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143;
Proc Natl Acad Sci U S A. 2016 Mar 22;113(12):E1645-54. doi: 10.1073/pnas.1514030113. Epub 2016 Feb 29.
The surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. Previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. We reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors. Upon complete consumption of ATP, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. These depend on actin concentration, filament length, and actin/myosin ratio. During formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. Regeneration of ATP supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. In a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phase-segregating domains. These results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization.
活细胞的表面为受体信号传导、蛋白质分选、运输和内吞作用提供了一个平台，其调节需要对膜组织进行局部控制。先前的研究揭示了动态肌动球蛋白在膜蛋白和脂质组织中的作用，这表明细胞表面表现为一种由流体双层和活性肌动球蛋白薄膜组成的活性复合物。我们在体外重建了一个类似的系统，该系统由一个流体脂质双层通过膜相关肌动蛋白结合蛋白与动态肌动蛋白丝和肌球蛋白马达耦合而成。在ATP完全消耗后，该系统进入肌动蛋白组织的不同阶段，即束状丝、连接的非极性星状体和极性星状体晶格。这些阶段取决于肌动蛋白浓度、丝长度和肌动蛋白/肌球蛋白比率。在极性星状体阶段形成过程中，自组织肌动球蛋白网络的平流驱动肌动蛋白相关膜成分的瞬时聚集。ATP的再生支持一种组成性重塑的肌动球蛋白状态，这反过来又驱动耦合膜成分的活性波动，类似于在细胞表面观察到的波动。在多组分膜双层中，这种重塑的肌动球蛋白层有助于相分离域的范围和动力学变化。这些结果表明局部膜组成是如何由肌动球蛋白产生的活性过程驱动的，突出了细胞表面活性复合物模型的基本基础，并表明其与膜组织研究的相关性。
