Shuttling between two protein conformations: the common mechanism for sensory transduction and ion transport.

It has recently become known that light-dependent interconversions between two protein conformations underlie both ion transport in bacteriorhodopsin and halorhodopsin and phototaxis signaling by the sensory rhodopsins of halobacteria. In the transport proteins, the two conformations facilitate alternating access of an occluded ion-binding site to the two surfaces of the membrane, and in the sensory receptors the conformations modulate signal-transducer activity. In sensory rhodopsin I, the same conformational equilibrium is implicated in providing both sensory signaling when bound to its transducer and proton transport when free.