The multiple faces of self-assembled lipidic systems

Lipids, the building blocks of cells, common to every living organisms, have the propensity to self-assemble into well-defined structures over short and long-range spatial scales. The driving forces have their roots mainly in the hydrophobic effect and electrostatic interactions. Membranes in lamellar phase are ubiquitous in cellular compartments and can phase-separate upon mixing lipids in different liquid-crystalline states. Hexagonal phases and especially cubic phases can be synthesized and observed in vivo as well. Membrane often closes up into a vesicle whose shape is determined by the interplay of curvature, area difference elasticity and line tension energies, and can adopt the form of a sphere, a tube, a prolate, a starfish and many more. Complexes made of lipids and polyelectrolytes or inorganic materials exhibit a rich diversity of structural morphologies due to additional interactions which become increasingly hard to track without the aid of suitable computer models. From the plasma membrane of archaebacteria to gene delivery, self-assembled lipidic systems have left their mark in cell biology and nanobiotechnology; however, the underlying physics is yet to be fully unraveled

Evidence that membrane curvature distorts the tertiary structure of bacteriorhodopsin

The membrane protein bacteriorhodopsin (bR) can be reconstituted into the membrane of the lipid 1-monoolein (MO). This lipid forms a lyotropic liquid crystalline phase whose membrane has hyperbolic interfacial curvature. Using optical absorption spectroscopy and small angle X-ray scattering we have observed retinal unbinding from bR that is correlated with the degree of membrane interfacial curvature. The evidence suggests that bR is susceptible to membrane induced saddle splay for modest perturbations from equilibrium, but for more extreme distortions becomes stiff and resists membrane induced curvature