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FOR THE RECORD

Crystallization of bacteriorhodopsin from bicelle formulations at room temperature

Department of Chemistry and Biochemistry, UCLA-DOE Center for Genomics and Proteomics, Molecular Biology Institute, University of California, Los Angeles (UCLA), California 90095-1570, USA

(RECEIVED October 7, 2004; FINAL REVISION November 23, 2004; ACCEPTED November 29, 2004)

We showed previously that high-quality crystals of bacteriorhodopsin (bR) from Halobacterium salinarum can be obtained from bicelle-forming DMPC/CHAPSO mixtures at 37°C. As many membrane proteins are not sufficiently stable for crystallization at this high temperature, we tested whether the bicelle method could be applied at a lower temperature. Here we show that bR can be crystallized at room temperature using two different bicelle-forming compositions: DMPC/CHAPSO and DTPC/CHAPSO. The DTPC/CHAPSO crystals grown at room temperature are essentially identical to the previous, twinned crystals: space group P2₁ with unit cell dimensions of a = 44.7 Å, b = 108.7 Å, c = 55.8 Å, = 113.6°. The room-temperature DMPC/CHAPSO crystals are untwinned, however, and belong to space group C222₁ with the following unit cell dimensions: a = 44.7 Å, b = 102.5 Å, c = 128.2 Å. The bR protein packs into almost identical layers in the two crystal forms, but the layers stack differently. The new untwinned crystal form yielded clear density for a previously unresolved CHAPSO molecule inserted between protein subunits within the layers. The ability to grow crystals at room temperature significantly expands the applicability of bicelle crystallization.

Keywords: membrane protein; lipid cubic phase; crystallization method; twinning

Abbreviations: bR, bacteriorhodopsin • DMPC, 1,2 dimyristoyl-sn-glycerol-3-phosphocholine • CHAPSO, 3[(3-cholamidopropyl) dimethylammonio]-2-hydroxy-1-propanesulfonate • DTPC, 1,2 ditridecanoyl-sn-glycerol-3-phosphocholine • DHPC, 1, 2 dihexanoyl-sn-glycero-3-phosphocholine

Article published online ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.041167605.

Reprint requests to: James U. Bowie, 655 Boyer Hall, 611 Charles E. Young Drive E., UCLA, Los Angeles, CA 90095-1570, USA; e-mail: bowie{at}mbi.ucla.edu; fax: (310) 206-4749.

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