Membrane Protein Crystallization From Cubic Lipid Matrices

Our projectThere are two intriguing questions that are raised by theLandau groups experiments. The first is whether thecubic structure they used is important, or whethersimply being in a membrane allows the membraneprotein to crystallize. Second, and more fundamental,is how the protein actually forms crystals. There areseveral clues to how this might work, but there are nohard answers.Two important lipid phases, (1)It may be that the precipitant is not directlyresponsible for the change in solubility that leadsto crystallization. There is indirect evidence thatthe crystals form due to structural changes in thesurrounding lipid matrix. We are exploringwhether changes in lipid crystal phase and latticeparameters lead to protein crystal formation.One of the challenges we face is that the complicated detergent-salt system which permits us to solubilizethe protein initially can interfere with the structural behavior of the lipids. Indeed, the designer detergentsused in membrane protein experiments are designed to have properties quite similar to those of lipids. It isnow well known that these detergents do alter the phase behavior of common lipids significantly. However,it may be possible to avoid the use of these detergents entirely. This is a question which remainsunanswered.(1)