Interactions between proteins bound to biomembranes

We study a physical model for the interaction between general inclusions bound to fluid membranes that possess finite tension, as well as the usual bending rigidity. We are motivated by an interest in proteins bound to cell membranes that apply forces to these membranes, due to either entropic or direct chemical interactions. We find an exact analytic solution for the repulsive interaction between two similar circularly symmetric inclusions. This repulsion extends over length scales of order tens of nanometers, and contrasts with the membrane-mediated contact attraction for similar inclusions on tensionless membranes. For non circularly symmetric inclusions we study the small, algebraically long-ranged, attractive contribution to the force that arises. We discuss the relevance of our results to biological phenomena, such as the budding of caveolae from cell membranes and the striations that are observed on their coats.Comment: 22 pages, 2 figure

Interaction forces and adhesion of supported myelin lipid bilayers modulated by myelin basic protein

Force–distance measurements between supported lipid bilayers mimicking the cytoplasmic surface of myelin at various surface coverages of myelin basic protein (MBP) indicate that maximum adhesion and minimum cytoplasmic spacing occur when each negative lipid in the membrane can bind to a positive arginine or lysine group on MBP. At the optimal lipid/protein ratio, additional attractive forces are provided by hydrophobic, van der Waals, and weak dipolar interactions between zwitterionic groups on the lipids and MBP. When MBP is depleted, the adhesion decreases and the cytoplasmic space swells; when MBP is in excess, the bilayers swell even more. Excess MBP forms a weak gel between the surfaces, which collapses on compression. The organization and proper functioning of myelin can be understood in terms of physical noncovalent forces that are optimized at a particular combination of both the amounts of and ratio between the charged lipids and MBP. Thus loss of adhesion, possibly contributing to demyelination, can be brought about by either an excess or deficit of MBP or anionic lipids

Liposome adhesion generates traction stress

International audienceMechanical forces generated by cells modulate global shape changes required for essential life processes, such as polarization, division and spreading. Although the contribution of the cytoskeleton to cellular force generation is widely recognized, the role of the membrane is considered to be restricted to passively transmitting forces. Therefore, the mechanisms by which the membrane can directly contribute to cell tension are overlooked and poorly understood. To address this, we directly measure the stresses generated during liposome adhesion. We find that liposome spreading generates large traction stresses on compliant substrates. These stresses can be understood as the equilibration of internal, hydrostatic pressures generated by the enhanced membrane tension built up during adhesion. These results underscore the role of membranes in the generation of mechanical stresses on cellular length scales and that the modulation of hydrostatic pressure due to membrane tension and adhesion can be channelled to perform mechanical work on the environment