1M0M

BACTERIORHODOPSIN M1 INTERMEDIATE AT 1.43 A RESOLUTION

Summary for 1M0M

• Entry DOI: 10.2210/pdb1m0m/pdb
• Related: 1m0k 1mol
• Descriptor: BACTERIORHODOPSIN, RETINAL, 1-[2,6,10.14-TETRAMETHYL-HEXADECAN-16-YL]-2-[2,10,14-TRIMETHYLHEXADECAN-16-YL]GLYCEROL, ... (5 entities in total)
• Functional Keywords: ion pump, membrane protein, retinal protein, lipids, photoreceptor, haloarchaea, 7-transmembrane, serpentine, merohedral twinning, ion transport
• Biological source: Halobacterium salinarum
• Cellular location: Cell membrane; Multi-pass membrane protein: P02945
• Total number of polymer chains: 1
• Total formula weight: 37243.94

Authors

Lanyi, J.K. (deposition date: 2002-06-13, release date: 2002-09-11, Last modification date: 2024-11-20)

Primary citation

Lanyi, J.,Schobert, B.
Crystallographic structure of the retinal and the protein after deprotonation of the Schiff base: the switch in the bacteriorhodopsin photocycle.
J.Mol.Biol., 321:727-737, 2002

PubMed Abstract: We illuminated bacteriorhodopsin crystals at 210K to produce, in a photostationary state with 60% occupancy, the earliest M intermediate (M1) of the photocycle. The crystal structure of this state was then determined from X-ray diffraction to 1.43 A resolution. When the refined model is placed after the recently determined structure for the K intermediate but before the reported structures for two later M states, a sequence of structural changes becomes evident in which movements of protein atoms and bound water are coordinated with relaxation of the initially strained photoisomerized 13-cis,15-anti retinal. In the K state only retinal atoms are displaced, but in M1 water 402 moves also, nearly 1A away from the unprotonated retinal Schiff base nitrogen. This breaks the hydrogen bond that bridges them, and initiates rearrangements of the hydrogen-bonded network of the extracellular region that develop more fully in the intermediates that follow. In the M1 to M2 transition, relaxation of the C14-C15 and C15=NZ torsion angles to near 180 degrees reorients the retinylidene nitrogen atom from the extracellular to the cytoplasmic direction, water 402 becomes undetectable, and the side-chain of Arg82 is displaced strongly toward Glu194 and Glu204. Finally, in the M2 to M2' transition, correlated with release of a proton to the extracellular surface, the retinal assumes a virtually fully relaxed bent shape, and the 13-methyl group thrusts against the indole ring of Trp182 which tilts in the cytoplasmic direction. Comparison of the structures of M1 and M2 reveals the principal switch in the photocycle: the change of the angle of the C15=NZ-CE plane breaks the connection of the unprotonated Schiff base to the extracellular side and establishes its connection to the cytoplasmic side.

PubMed: 12206786
DOI: 10.1016/S0022-2836(02)00682-4

Experimental method

X-RAY DIFFRACTION (1.43 Å)