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Proc Natl Acad Sci U S A. 2016 Mar 22;113(12):E1645-54. doi: 10.1073/pnas.1514030113. Epub 2016 Feb 29.

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer.

Author information

1
National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India;
2
Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143;
3
National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India; Raman Research Institute, Bangalore 560080, India;
4
National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India; Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India mayor@ncbs.res.in.

Abstract

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.

KEYWORDS:

actin; active mechanics; membrane organization; myosin II

PMID:
26929326
PMCID:
PMC4812753
DOI:
10.1073/pnas.1514030113
[Indexed for MEDLINE]
Free PMC Article

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