Crystal structure of squid rhodopsin

Nature. 2008 May 15;453(7193):363-7. doi: 10.1038/nature06925.


Invertebrate phototransduction uses an inositol-1,4,5-trisphosphate signalling cascade in which photoactivated rhodopsin stimulates a G(q)-type G protein, that is, a class of G protein that stimulates membrane-bound phospholipase Cbeta. The same cascade is used by many G-protein-coupled receptors, indicating that invertebrate rhodopsin is a prototypical member. Here we report the crystal structure of squid (Todarodes pacificus) rhodopsin at 2.5 A resolution. Among seven transmembrane alpha-helices, helices V and VI extend into the cytoplasmic medium and, together with two cytoplasmic helices, they form a rigid protrusion from the membrane surface. This peculiar structure, which is not seen in bovine rhodopsin, seems to be crucial for the recognition of G(q)-type G proteins. The retinal Schiff base forms a hydrogen bond to Asn 87 or Tyr 111; it is far from the putative counterion Glu 180. In the crystal, a tight association is formed between the amino-terminal polypeptides of neighbouring monomers; this intermembrane dimerization may be responsible for the organization of hexagonally packed microvillar membranes in the photoreceptor rhabdom.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Crystallography, X-Ray
  • Decapodiformes / chemistry*
  • Dimerization
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Structure, Secondary
  • Retinaldehyde / metabolism
  • Rhodopsin / chemistry*
  • Rhodopsin / metabolism
  • Schiff Bases
  • Vision, Ocular / physiology
  • Water / chemistry
  • Water / metabolism


  • Schiff Bases
  • Water
  • Rhodopsin
  • Retinaldehyde

Associated data

  • PDB/2Z73