ABSTRACT
Retinal photoreceptor proteins for visual function comprise one of the large subfamilies in class A G protein-coupled receptors (GPCRs). Rhodopsin in the rod cells is the best studied and represents a paradigm for understanding the structure and function of GPCRs. The heptahelical transmembrane motif shared by all GPCRs was first demonstrated by electron cryomicroscopy of bovine rhodopsin in two-
dimensional crystals.
