1m0l
From Proteopedia
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BACTERIORHODOPSIN/LIPID COMPLEX AT 1.47 A RESOLUTION
Overview
The K state, an early intermediate of the bacteriorhodopsin photocycle, contains the excess free energy used for light-driven proton transport., The energy gain must reside in or near the photoisomerized retinal, but in, what form has long been an open question. We produced the K intermediate, in bacteriorhodopsin crystals in a photostationary state at 100K, with 40%, yield, and determined its X-ray diffraction structure to 1.43 A, resolution. In independent refinements of data from four crystals, the, changes are confined mainly to the photoisomerized retinal. The retinal is, 13-cis,15-anti, as known from vibrational spectroscopy. The C13=C14 bond, is rotated nearly fully to cis from the initial trans configuration, but, the C14-C15 and C15=NZ bonds are partially counter-rotated. This strained, geometry keeps the direction of the Schiff base N-H bond vector roughly in, the extracellular direction, but the angle of its hydrogen bond with water, 402, that connects it to the anionic Asp85 and Asp212, is not optimal., Weakening of this hydrogen bond may account for many of the reported, features of the infrared spectrum of K, and for its photoelectric signal, as well as the deprotonation of the Schiff base later in the cycle., Importantly, although 13-cis, the retinal does not assume the expected, bent shape of this configuration. Comparison of the calculated energy of, the increased angle of C12-C13=C14, that allows this distortion, with the, earlier reported calorimetric measurement of the enthalpy gain of the K, state indicates that a significant part of the excess energy is conserved, in the bond strain at C13.
About this Structure
1M0L is a Single protein structure of sequence from Halobacterium salinarum with LI1, SQU and RET as ligands. Full crystallographic information is available from OCA.
Reference
Crystallographic structure of the K intermediate of bacteriorhodopsin: conservation of free energy after photoisomerization of the retinal., Schobert B, Cupp-Vickery J, Hornak V, Smith S, Lanyi J, J Mol Biol. 2002 Aug 23;321(4):715-26. PMID:12206785
Page seeded by OCA on Tue Nov 20 21:02:21 2007
