Rhodopsin is the archetypal G-protein-coupled receptor. Such receptors participate in virtually all physiological processes, as signalling molecules. They utilise heterotrimeric guanosine triphosphate (GTP)-binding proteins to transduce extracellular signals to intracellular events. Rhodopsin is important because of the pivotal role it plays in visual signal transduction. Rhodopsin is a dimeric transmembrane protein and its intradiskal surface consists of this amino terminal domain and three loops connecting six of the seven transmembrane helices. The N-terminus is a compact domain of alpha-helical regions with breaks and bends at proline residues outside the membrane [1]. The transmembrane part of rhodopsin is represented by 7tm_1 (Pfam:PF00001). The N-terminal domain is extracellular is and is necessary for successful dimerisation and molecular stability [2].

1: Structures of the intradiskal loops and amino terminus of the G-protein receptor, rhodopsin. Yeagle PL, Salloum A, Chopra A, Bhawsar N, Ali L, Kuzmanovski G, Alderfer JL, Albert AD; J Pept Res. 2000;55:455-465. PMID:10888202

2: Structure of the rhodopsin dimer: a working model for G-protein-coupled receptors. Fotiadis D, Jastrzebska B, Philippsen A, Muller DJ, Palczewski K, Engel A; Curr Opin Struct Biol. 2006;16:252-259. PMID:16567090