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J. Biol. Chem., Vol. 283, Issue 26, 17753-17756, June 27, 2008

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Crystal Structure of Squid Rhodopsin with Intracellularly Extended Cytoplasmic Region^*

Tatsuro Shimamura¹, Kenji Hiraki¹, Naoko Takahashi, Tetsuya Hori, Hideo Ago, Katsuyoshi Masuda, Koji Takio, Masaji Ishiguro², and Masashi Miyano³

From the RIKEN SPring-8 Center, Harima Institute, Kouto, Sayo, Hyogo 679-5148 and the Suntory Institute for Bioorganic Research, 1-1-1 Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka 618-8503, Japan

G-protein-coupled receptors play a key step in cellular signal transduction cascades by transducing various extracellular signals via G-proteins. Rhodopsin is a prototypical G-protein-coupled receptor involved in the retinal visual signaling cascade. We determined the structure of squid rhodopsin at 3.7Å resolution, which transduces signals through the G_q protein to the phosphoinositol cascade. The structure showed seven transmembrane helices and an amphipathic helix H8 has similar geometry to structures from bovine rhodopsin, coupling to G_t, and humanβ₂-adrenergic receptor, coupling to G_s. Notably, squid rhodopsin contains a well structured cytoplasmic region involved in the interaction with G-proteins, and this region is flexible or disordered in bovine rhodopsin and humanβ₂-adrenergic receptor. The transmembrane helices 5 and 6 are longer and extrude into the cytoplasm. The distal C-terminal tail contains a short hydrophilic -helix CH after the palmitoylated cysteine residues. The residues in the distal C-terminal tail interact with the neighboring residues in the second cytoplasmic loop, the extruded transmembrane helices 5 and 6, and the short helix H8. Additionally, the Tyr-111, Asn-87, and Asn-185 residues are located within hydrogen-bonding distances from the nitrogen atom of the Schiff base.

Received for publication, February 5, 2008 , and in revised form, April 15, 2008.

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The atomic coordinates and structure factors (code 2ZIY) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental text and two supplemental figures.

¹ Both authors contributed equally to this work.

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² To whom correspondence may be addressed. E-mail: ishiguro{at}sunbor.or.jp. ³To whom correspondence may be addressed. E-mail: miyano{at}spring8.or.jp.

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