Polymorphism of Cross-Linked Actin Networks in Giant Vesicles

Actin networks cross-linked by natural linkers $\alpha$-actinin and filamin are generated in giant vesicles by polymerization through ionophore-mediated influx of ${\mathrm{M}\mathrm{g}}^{2+}$. $\alpha$-actinin induces the formation of randomly linked networks at 25 °C which transform at $<15°\mathrm{C}$ into spiderweblike gels or ringlike bundles depending on the vesicle size. Muscle filamin forms ringlike structures under all experimental conditions which can supercoil by subsequent ${\mathrm{M}\mathrm{g}}^{2+}$ addition. The polymorphism is rationalized in terms of recent models of bivalent ion coupled semiflexible polyelectrolytes and by considering the topology of the linkers.