Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 413, Issue 3, Pages 615-627Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2011.08.044
Keywords
visual transduction; G-protein-coupled receptor; retinal; seven-transmembrane protein; X-ray damage
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Funding
- Ministry of Education, Science, and Culture of Japan
- Grants-in-Aid for Scientific Research [23121513, 22770146, 21370070] Funding Source: KAKEN
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Visual signal transduction is initiated by the photoisomerization of 11-cis retinal upon rhodopsin ligation. Unlike vertebrate rhodopsin, which interacts with Gt-type G-protein to stimulate the cyclic GMP signaling pathway, invertebrate rhodopsin interacts with Gq-type G-protein to stimulate a signaling pathway that is based on inositol 1,4,5-triphosphate. Since the inositol 1,4,5-triphosphate signaling pathway is utilized by mammalian nonvisual pigments and a large number of G-protein-coupled receptors, it is important to elucidate how the activation mechanism of invertebrate rhodopsin differs from that of vertebrate rhodopsin. Previous crystallographic studies of squid and bovine rhodopsins have shown that there is a profound difference in the structures of the retinal-binding pockets of these photoreceptors. Here, we report the crystal structures of all-trans bathorhodopsin (Batho; the first photoreaction intermediate) and the artificial 9-cis isorhodopsin (Iso) of squid rhodopsin. Upon the formation of Batho, the central moiety of the retinal was observed to move largely towards the cytoplasmic side, while the Schiff base and the ionone ring underwent limited movements (i.e., the all-trans retinal in Batho took on a right-handed screwed configuration). Conversely, the 9-cis retinal in Iso took on a planar configuration. Our results suggest that the light energy absorbed by squid rhodopsin is mostly converted into the distortion energy of the retinal polyene chain and surrounding residues. (C) 2011 Elsevier Ltd. All rights reserved.
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