Rab proteins and post Golgi trafficking of rhodopsin in photoreceptor cells

Polarized sorting of rhodopsin in retinal rod photoreceptors is mediated by post-Golgi vesicles that bud from the trans-Golgi network and fuse with the specialized domain of the plasma membrane in the rod inner segment. This domain surrounds the cilium that connects the inner segment and the rod outer segment to which mature rhodopsin is delivered. To dissect the sorting machinery that regulates budding, targeting, and fusion of rhodopsin carrier vesicles, their GTP-binding protein composition has been studied using multiple means including high-resolution two-dimensional gel electrophoresis and [P-32]GTP overlays of renatured proteins. These studies indicate a succession on rhodopsin-bearing vesicles of rab6, rab11, rab3 and rab8, all members of the small GTP-binding protein family of the known regulators of membrane trafficking. In this review the role of rab proteins in post-Golgi trafficking of rhodopsin is discussed.