Ordered stacking of F-actin layers and mixed lipid bilayers: a columnar liquid crystal

In this Letter, we show how the grooved helical structure of actin microfilaments (F-actin) interacting with mixed fluid lipid bilayers leads to handedness-independent 1D lipid bilayer undulations coupled to longitudinal in-plane ordering of the microfilaments. This longitudinal ordering is forced by the emerging in-plane compression and curvature energy terms of the straight 1D bilayer undulation wave fronts. Thereby, adjacent helices are set into registry along their long axis in their monolayer and π shifted between adjacent monolayers. An ordered composite multilamellar structure emerges by alternate stacking of these lipid bilayers and monolayers of F-actin. This two-dimensionally ordered system has the symmetries of a centered rectangular columnar liquid crystal, the straight 1D wave fronts playing the role of the classical molecular columns.

Thermal diffuse x-ray scattering in a model columnar liquid crystal

The fluctuation correlation functions and the density-density correlation functions for a realistic model of a columnar liquid crystal in its helically ordered phase are derived. The influence of positional and orientational molecular fluctuations on the thermal diffuse x-ray scattering is studied within a three-dimensional model of columns inscribed on a triangular lattice. Resulting from quasi-long-range ordering, very anisotropic long-tail scattered intensities are predicted, giving a nonuniversal signature for the helically ordered columnar liquid crystal phase. Scattered intensities both near the Bragg maxima at the inverse lattice vectors and at the Bragg condition due to periodic orientational ordering are treated. The percolation of the long-range behavior for a screw variable composed of two quantities having only quasi-long-range behavior is predicted.