Molecular mechanism for the crystallization of bacteriorhodopsin in lipidic cubic phases

Nollert, Peter; Qiu, Hong; Caffrey, Martin; Rosenbusch, Jurg P; Landau, Ehud M

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Volume 504, Issue 3 , Pages 179-186, 31 August 2001

Molecular mechanism for the crystallization of bacteriorhodopsin in lipidic cubic phases

Edited by Andreas Engel and Giorgio Semenza

Peter Nollert
- Department of Biochemistry and Biophysics, University of California San Francisco, 513 Parnassus, San Francisco, CA 94134-0448, USA
- Biozentrum, University of Basel, Klingelbergstr. 70, CH-4056 Basel, Switzerland
Hong Qiu
- Biochemistry, Biophysics, Chemistry, Ohio State University, 100 W. 18th Avenue, Columbus, OH 43210, USA
Martin Caffrey
- Biochemistry, Biophysics, Chemistry, Ohio State University, 100 W. 18th Avenue, Columbus, OH 43210, USA
Jurg P Rosenbusch
- Biozentrum, University of Basel, Klingelbergstr. 70, CH-4056 Basel, Switzerland
Ehud M Landau
- Biozentrum, University of Basel, Klingelbergstr. 70, CH-4056 Basel, Switzerland
- Department of Physiology and Biophysics, Membrane Protein Laboratory, and Sealy Center for Structural Biology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0641, USA
- Corresponding author. Department of Physiology and Biophysics, 301 University Blvd., University of Texas Medical Branch, Galveston, TX 77555-0437, USA. Fax: (1)-409-772 1301

Received 11 July 2001; accepted 23 July 2001.

Abstract

Crystals of transmembrane proteins may be grown from detergent solutions or in a matrix of membranous lipid bilayers existing in a liquid crystalline state and forming a cubic phase (in cubo). While crystallization in micellar solutions appears analogous to that for soluble proteins, crystallization in lipidic matrices is poorly understood. As this method was shown to be applicable to several membrane proteins, understanding its mechanism will facilitate a rational design of crystallization, minimizing the laborious screening of a large number of parameters. Using polarization microscopy and low-angle X-ray diffraction, experimental evidence is provided to support a mechanistic model for the in cubo crystallization of bacteriorhodopsin in a lipid matrix. Membrane proteins are thought to reside in curved lipid bilayers, to diffuse into patches of lower curvature and to incorporate into lattices which associate to form highly ordered three-dimensional crystals. Critical testing of this model is necessary to generalize it to other membrane proteins.

Keywords: Crystallization, Bacteriorhodopsin, Lipidic cubic phases

Abbreviations: bR, bacteriorhodopsin, MO, monoolein, OG, β-octyl glucopyranoside