Physical detwinning of hemihedrally twinned hexagonal crystals of bacteriorhodopsin

Abstract

Hexagonal crystals of the membrane protein bacteriorhodopsin of space group P63 grown in lipidic cubic phase are twinned hemihedrally. It was shown that slow changes of salt concentration in the mother liquor lead to a split of crystals so that the split parts preserved high diffraction quality. Analysis of diffraction data from split crystals by Yeates statistic and Britton plot showed that the split parts are free of twinning. It is concluded that crystals of bacteriorhodopsin are composed of several macroscopic twinning domains with sizes comparable to the original crystal. The appearance of twinning domains during crystal growth and the mechanism of splitting are discussed. © 2004 by the Biophysical Society.