The assembly of two-dimensional membrane protein crystals in the presence of lipids was analyzed with quasielastic light scattering and electron microscopy. Mixtures of detergent-solubilized lipids and/or proteins were submitted to slow or rapid dilution while measuring the hydrodynamic radii of the aggregates. Lipids alone exhibited λ-shaped dilution curves with intermediate rod-shaped particles that converted into small vesicles. Depending on the protein-protein and protein-lipid interactions, detergent-solubilized protein-lipid mixtures showed a sharp transition from micelles to large, densely packed proteoliposomes. Electron microscopy revealed that formation of crystals occurred shortly after this phase transition.
