Skin layer at the actin-gel surface: quenched protein membranes form flat, crumpled, and tubular morphologies.

We report the discovery of a hierarchically structured skin layer formed at the surface of an isotropic gel of filamentous actin bundles at high molar ratios of alpha-actinin, an actin cross-linker, to globular actin. Confocal microscopy has elucidated the full, micron scale 3D structure. The protein skin layer, composed of a directed network of bundles, exhibits flat, crumpled, tubelike and pleated multitubular morphologies, resulting from stresses due to the underlying gel. The skin layer, which readily detaches, constitutes a model anisotropic solid membrane with stress-induced, quenched disorder.