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Abstract:
ATPases are a group of enzymes that can cyclically convert the free energy of
ATP hydrolysis into mechanical work. GTPases are another class of enzymes
that are predominantly associated with signal transduction processes, but
their role in mechanotransduction is less established. It was previously
shown that the binding of the GTPase Rab5 to the tethering protein EEA1
induces a large conformational change in EEA1 from a rigid, extended to
a flexible, collapsed state. This entropic collapse of EEA1 gives rise to an
effective force that can pull tethered membranes closer. It currently remains
unclear if EEA1 can return from the collapsed to the extended conformation
without the aid of chaperone proteins. Here we show that EEA1 in a bulk
solution can undergo multiple flexibility transition cycles driven by the
energetics of Rab5 binding and unbinding as well as GTP hydrolysis. Each
cycle can perform up to 20kBT of mechanical work. Hence, Rab5 and EEA1
constitute a two-component molecular motor driven by the chemical
energy derived from the Rab5 GTPase cycle. We conclude that tethering
proteins and their small GTPase partners can have active mechanical roles
in membrane trafficking.
