Synthetic rhodopsin analogs

A great variety of synthetic retinals have been bound to rhodopsins, both in vitro and in vivo; they have also been incorporated into bacteriorhodopsin and other sensory pigments. The structural variations in these retinal analogs are numerous and include chromophores that are hydrogenated, acyclic, contain extra rings, carry special groups such as photoaffimty labels, or are isotopically labeled. The structures of retinal analogs are designed so that they can provide answers to specific questions regarding the structure, function, mode of action of the native pigments. Although the syntheses and binding of analogs, physical measurements, biochemical and biological studies of such rhodopsin analogs are frequently very challenging, the results yield crucial information. The various visual pigment analogs are reviewed in the following.