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The surface of a living cell provides a platform for processes such
as receptor signaling, proteinsorting, transport and endocytosis. The
regulation of these processes requires the controllableorganisation
of membrane components. A recent framework for the organisation of a
certain classof plasma membrane components is based on the active
mechanics of acto-myosin juxtaposed to themembrane (Gowrishankar *et
al.*, 2012; Rao & Mayor, 2014). A systematic study of the dynamics
and consequences of this active compositein living cells is
challenging. Here we reconstitute an active composite in vitro, by a
stepwise additionof the minimal
ingredients: a supported lipid bilayer with an actin-binding
component, short actinfilaments and myosin motors. By systematically
varying the concentrations of actin and myosin
as well as the level of ATP we find a rich phase diagram of
membrane-confined actin and myosinconfigurations. By increasing the
level of available ATP we induce a constitutively remodeling
state,in which asters composed of short actin filaments form and
dissolve. In this state, the coupling ofactin to the bilayer drives
the membrane components out of equilibrium, imparting distinct
signaturesof activity in a manner entirely consistent with
measurements in the living cell. These results highlightthe
fundamental basis of the active composite framework and indicate its
relevance in the study
ofmembrane organisation. |