Detergent-free membrane protein crystallization.

A comprehensive understanding of structure-function relationships of proteins requires their structures to be elucidated to high resolution. With most membrane proteins this has not been accomplished so far, mainly because of their notoriously poor crystallizability. Here we present a completely detergent-free procedure for the incorporation of a native purple membrane into a monoolein-based lipidic cubic phase, and subsequent crystallization of three-dimensional bacteriorhodopsin crystals therein. These crystals exhibit comparable X-ray diffraction quality and mosaicity, and identical crystal habit and space group to those of bacteriorhodopsin crystals that are grown from detergent-solubilized protein in cubic phase.