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 Mg2+. alpha-actinin induces the formation of randomly linked networks at 25 degrees C which transform at <15 degrees 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 Mg2+ addition. The polymorphism is rationalized in terms of recent models of bivalent ion coupled semiflexible polyelectrolytes and by considering the topology of the linkers.