The method: cubic lipid phase (CLP) crystallization, developed by E. Landau & G. Rosenbusch (PNAS, 1996). The detergent-solubilized membrane protein is added to the CLP matrix where it partitions into the hydrophobic phase. Since the hydrophobic phase has bilayer topology, the protein is assumed to be a lot "happier" in it than in detergent micelles. Addition of a precipitant causes crystal nucleation & growth which is facilitated by controlled lateral diffusion in the three-dimensional bicontinuous matrix.
The crystals: purple crystals appear after a few days, usually hundreds of them in a single set-up. The crystals form small hexagonal plates about 80 um x 80 um x 15 um. They are very stable and can easily be transported in the CLP matrix. The layers in the a/b plane of the 3-dimensional BR crystals formed in CLP are very similar to the naturally occurring 2-D crystals sheets of BR in purple membranes. The space group is P63 with a=b=61 Å, c=108 Å and two trimers per unit cell. They diffract to 2.3 Å at the home lab, to 2.05 Å at beam line 9-1 at the Stanford Synchrotron (SSRL), and most recently to 1.40 Å (10 sigma spots) at beamline 5.0.2 at the Advanced Light Source (ALS) and to 1.33 Å at the microfocus beamline (ID13) at the European Synchrotron Research Facility (ESRF). The P63 CLP crystals are heavily merohedrally twinned and thus require special consideration during refinement.
Proton Transfer Pathways in Bacteriorhodopsin at 2.3 Angstrom Resolution.
H Luecke, H-T Richter, JK Lanyi (1998) Science 280, 1934-1937.
Structure of Bacteriorhodopsin at 1.55 Angstrom Resolution.
H Luecke, B Schobert, H-T Richter, JP Cartailler, JK Lanyi (1999) J. Mol. Biol. 291, 899-911.
The atomic models:
1brx.pdb (released on Aug 25, 1998): 2.3 Å light-adapted wild-type structure described in the 1998 Science paper.
(released on Jul 31, 1999): 1.55 Å light-adapted wild-type
structure described in the 1999 JMB paper.