Crystal structure of squid rhodopsin

Midori Murakami and Tsutomu Kouyama ()
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Midori Murakami: Graduate School of Science, Nagoya University
Tsutomu Kouyama: Graduate School of Science, Nagoya University

Nature, 2008, vol. 453, issue 7193, 363-367

Abstract: Abstract Invertebrate phototransduction uses an inositol-1,4,5-trisphosphate signalling cascade in which photoactivated rhodopsin stimulates a Gq-type G protein, that is, a class of G protein that stimulates membrane-bound phospholipase Cβ. 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 Å resolution. Among seven transmembrane α-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 Gq-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.

Date: 2008
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DOI: 10.1038/nature06925

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