| Rhodopsin was the first G protein-coupled receptor (GPCR) for which a high-resolution crystal structure
was obtained. Several crystal structures have now been solved representing different activation states
of the receptor. These structures, together with those from lower resolution techniques (e.g. electron
microscopy), shed light on the stepwise process by which energy from an extracellular photon is transduced
across the membrane to the intracellular compartment thereby activating signalling mechanisms
responsible for very low-level light detection. Controversy remains in several areas including: (i) transmembrane
helix movements responsible for the transduction process, (ii) the stoichiometry of coupling
to G proteins and their mode of activation, (iii) the role, if any, of receptor oligomerisation and (iv) the
suitability of using structures of this GPCR as templates for modelling the structures of other GPCRs, and
their mechanisms of activation. |