Protein attraction in membranes induced by lipid fluctuations.

The nonspecific lipid-mediated attraction between two proteins embedded in a bilayer membrane have been investigated for a model system using Monte Carlo simulations. We found two types of attraction with different regimes. A depletion-induced attraction in the range r < sigmaL, where sigmaL is the diameter of a lipid and r is the distance between the surfaces of the two proteins, and a fluctuation-induced attraction in the range 1 < r/sigmaL < 6, which originates from the gradients of density and orientational fluctuations of the lipids around each protein. The effective potential of the latter type of attraction decays exponentially with U(r) approximately exp(r/vi) where the correlation length is vi/sigmaL approximately 3.2 in the present model system.