Experimental Evidence for Membrane-Mediated Protein-Protein Interaction

Membrane proteins diffuse within the membrane, form oligomers and supramolecular assemblies. Using highspeed atomic force microscopy, we present direct experimental measure of an in-membrane-plane interaction potential between membrane proteins. In purple membranes, ATP-synthase c-rings formed dimers that temporarily dissociated. C-ring dimers revealed subdiffusive motion, while dissociated monomers diffused freely. C-rings center-to-center distance probability distribution allowed the calculation and modeling of an in-membrane-plane energy landscape that presented repulsion at 80 A, most stable dimer association at 103 angstrom (-3.5 k(B) T strength), and dissociation at 125 angstrom (-1 k(B) T strength). This first experimental data of nonlabeled membrane protein diffusion and the corresponding in-membrane-plane interaction energy landscape characterized membrane protein interaction with an attractive range of several k(B)T that reaches to a radius of similar to 50 angstrom within the membrane plane.