3HAN TRANSPORT PROTEIN, BACTERIORHODOPSIN, PACKING FORCE, VAN DER WAALS, EVOLUTIONARY CONSTRAINT, MEMBRANE PROTEIN, INTEGRAL MEMBRANE PROTEIN, HELICAL MEMBRANE PROTEIN, PROTON TRANSPORT, CELL MEMBRANE, CHROMOPHORE, HYDROGEN ION TRANSPORT, ION TRANSPORT, MEMBRANE, PHOTORECEPTOR PROTEIN, PYRROLIDONE CARBOXYLIC ACID, RECEPTOR, RETINAL PROTEIN, SENSORY TRANSDUCTION, TRANSMEMBRANE, TRANSPORT CRYSTAL STRUCTURE OF BACTERIORHODOPSIN MUTANT V49A CRYSTALLIZED FROM BICELLES