nl9b02241_si_005.avi (521.13 kB)
Geometrical Constraints Greatly Hinder Formin mDia1 Activity
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posted on 2019-12-13, 18:13 authored by Emiko
L. Suzuki, Jahnavi Chikireddy, Serge Dmitrieff, Bérengère Guichard, Guillaume Romet-Lemonne, Antoine JégouFormins are one of the central players in the assembly
of most
actin networks in cells. The sensitivity of these processive molecular
machines to mechanical tension is now well established. However, how
the activity of formins is affected by geometrical constraints related
to network architecture, such as filament cross-linking and formin
spatial confinement, remains largely unknown. Combining microfluidics
and micropatterning, we reconstituted in vitro mDia1 formin-elongated
filament bundles induced by fascin, with different geometrical constraints
on the formins, and measured the impact of these constraints on formin
elongation rate and processivity. When filaments are not bundled,
the anchoring details of formins have only a mild impact on their
processivity and do not affect their elongation rate. When formins
are unanchored, we show that filament bundling by fascin reduces both
their elongation rate and their processivity. Strikingly, when filaments
elongated by surface-anchored formins are cross-linked together, formin
elongation rate immediately decreases and processivity is reduced
up to 24-fold depending on the cumulative impact of formin rotational
and translational freedom. Our results reveal an unexpected crosstalk
between the constraints at the filament and the formin levels. We
anticipate that in cells the molecular details of formin anchoring
to the plasma membrane strongly modulate formin activity at actin
filament barbed ends.