Phase behavior and interactions of the membrane-protein bacteriorhodopsin

Abstract

We present a synchrotron x-ray diffraction study of melting in stacks of two-dimensional crystalline arrays of the membrane protein bacteriorhodopsin. Two distinct regimes have been found as a function of the intermembrane distance d. In the "coupled" regime for d < 250 Angstrom the temperature (T-m) of the melting transition decreases with increasing d, demonstrating the effect of the repulsive membrane interactions on the intramembrane protein ordering. For d > 250 Angstrom a "decoupled" regime is found with higher T-m independent of d. Below T-m a solid-liquid-solid reentrant behavior is observed as d is increased.