Conformation Changes of a 7TM Receptor Caused by the Sample Environment as Studied by Multidisciplinary Biophysical Methods

Abstract

Choosing an appropriate sample environment is critical in structural biology, not only for trapping functionally relevant intermediate states of a membrane protein, but also for interrogation of structure, conformation and dynamics to elucidate structure-function relationships. Functional assays and structural studies should therefore be performed in the same environment.Bacteriorhodopsin (bR), a member of the microbial rhodopsin family 7TM proteins, acting as a light-driven proton pump for light energy capture in Halobacterium Salinarum, has been studied by multidisciplinary approaches to reveal the molecular machinery of proton transfer and photocycle. For example, in order to study the functionally related structural change in M-state intermediate, different media with a high pH value have been used to extend the lifetime of M state. However, not much attention have been paid to the conformational changes that occur in the ground state, especially around the retinal binding pocket, due to local environment.Here, the conformation changes to the bR ground state, especially around the retinal binding pocket, have been studied by solid-state NMR through chemical shifts and torsion angle measurements, combined with the light-induced kinetic and UV spectroscopies. All the experimental results have been discussed in the context of X-ray crystal structures, and possible mechanisms have been proposed.