The Amphipathic Helix in Visual Cycle Proteins: A Review

Abstract

The visual cycle is a complex biological process that involves the sequential action of proteins in the retinal pigment epithelial (RPE) cells and photoreceptors to modify and shuttle visual retinoids. A majority of the visual cycle proteins are membrane proteins, either integral or peripheral membrane proteins. Despite significant progress in understanding their physiological function, very limited structural information is available for the visual cycle proteins. Moreover, the mechanism of membrane interaction is not yet clear in all cases. Here, we demonstrate the presence of an amphipathic helix in selected RPE visual cycle proteins, using in silico tools, and highlight their role in membrane association and function.

Keywords: Alpha (α)-helix; Amphipathic helix; CRALBP; LRAT; Membrane association; RDH5; RPE65; Retinoids; Visual cycle proteins.

Fig. XX.1

A. Helical wheel representations of AH sequences of RPE-specific visual cycle proteins (RPE65, LRAT, CRALBP, RDH5, RDH10, and RDH11). The numbers in superscripts correspond to the residue positions of the predicted AH motif. B. Hydrophobic moment plot for the predicted AHs where each point represents an 18-residue α-helix.