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Bacteriorhodopsin/Amphipol Complexes: Structural and Functional Properties

Yann Gohon ^*, Tassadite Dahmane ^*, Rob W. H. Ruigrok , Peter Schuck , Delphine Charvolin ^*, Fabrice Rappaport , Peter Timmins ^¶, Donald M. Engelman ^||, Christophe Tribet ^**, Jean-Luc Popot ^* and Christine Ebel 

^* Laboratoire de Physico-Chimie Moléculaire des Membranes Biologiques, Centre National de la Recherche Scientifique (CNRS), and Université Paris-7, Institut de Biologie Physico-Chimique, Paris, France; Unit for Virus Host Cell Interactions, Grenoble, France; PBR, DBPS, ORS, National Institutes of Health, Bethesda, Maryland; CNRS and Université Paris-6, Institut de Biologie Physico-Chimique, Paris, France; ^¶ Large Scale Structures Group, Institut Laue-Langevin, Avenue des Martyrs, Grenoble, France; ^|| Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut; ^** Laboratoire de Physico-Chimie des Polymères et des Milieux Dispersés, CNRS, ESPCI, Paris, France; and CNRS, IBS, Laboratoire de Biophysique Moléculaire, CEA, DSV, IBS, and Université Joseph Fourier, Grenoble, France

Correspondence: Address reprint requests to Christine Ebel, IBS, 41 rue Jules Horowitz, Grenoble, F-38027, France. Tel.: 33-438789570; Fax: 33-438785494; E-mail: christine.ebel{at}ibs.fr; or Jean-Luc Popot, IBPC, 13 rue Pierre et Marie Curie, F-75005 Paris, France. Tel.: 33-158415004; Fax: 33-158415024; E-mail: jean-luc.popot{at}ibpc.fr.

The membrane protein bacteriorhodopsin (BR) can be kept soluble in its native state for months in the absence of detergent by amphipol (APol) A8-35, an amphiphilic polymer. After an actinic flash, A8-35-complexed BR undergoes a complete photocycle, with kinetics intermediate between that in detergent solution and that in its native membrane. BR/APol complexes form well defined, globular particles comprising a monomer of BR, a complete set of purple membrane lipids, and, in a peripheral distribution, 2 g APol/g BR, arranged in a compact layer. In the absence of free APol, BR/APol particles can autoassociate into small or large ordered fibrils.