Supramolecular structure of opsins

Abstract Opsins are G protein-coupled receptors present in photoreceptor cells of the retina that initiate vision upon activation by light. Cone opsins are present in cone photoreceptor cells and are responsible for photopic vision, whereas rhodopsin is present in rod photoreceptor cells and is responsible for scotopic vision. Due to the relative abundance of rod photoreceptor cells in most vertebrate retinas, our understanding about the structure and function of rhodopsin far exceeds that of cone opsins. Rhodopsin has been studied extensively for over a century, and our molecular and structural concept of the receptor has evolved over this time. The current molecular and structural concept of rhodopsin involves a supramolecular structure whereby the receptor exists in the membrane in nanodomains formed by oligomers of rhodopsin. This chapter focuses on our current understanding about the supramolecular architecture of rhodopsin in photoreceptor membranes and the modulation and functional implications of this structure. The developing understanding about the oligomerization of cone opsins is also discussed.