GENERAL-MODEL FOR LIPID-MEDIATED 2-DIMENSIONAL ARRAY FORMATION OF MEMBRANE-PROTEINS - APPLICATION TO BACTERIORHODOPSIN

Based on experimental evidence for 2D array formation of bacteriorhodo psin, we propose a general model for lipid-mediated 2D array formation of membrane proteins in lipid bilayers. The model includes two differ ent lipid Species; ''annular'' lipids and ''neutral'' lipids, and one protein species. The central assumption of the model is that the annul ar lipids interact more strongly with the protein than with the neutra l lipids. Monte Carlo simulations performed on this model show that 2D arrays of proteins only form when there are annular lipids present. I n addition, no arrays form if all of the lipids present are annular li pids. The geometry of the observed arrays is for the most part hexagon al. However, for a certain range of low annular lipid/protein ratios, arrays form that have geometries other than hexagonal. Using the assum ption that the hydrocarbon chains of the annular lipids are restricted in motion when close to a protein, we expand the model to include a g round state and an excited state of the annular lipids. The main resul t from the extended model is that within a certain temperature range, increasing the temperature will lead to larger and more regular protei n arrays.