BIOL 244 |
| Vertebrate visual pigments are G-protein coupled receptors (GPCR) that are composed of seven transmembrane helices and a chromophore attached to a conserved lysine residue through a Schiff base linkage. The absorption maxima of these pigments are dependent on the residues surrounding the retinal, the type of chromophore (A1 or A2) and the chromophore ring conformation (6-s-cis or 6-s-trans). The absorption maxima of mid- and long-wavelength sensitive (M/LWS) visual pigments are distributed mainly into two regions of the visible spectrum. The A1-containing pigments are populated at 520 nm and 564 nm, while the A2-containing pigments are populated at 532 nm and 620 nm. The excited state properties of the chromophore binding site models are obtained by using modified neglect of differential overlap with partial single and double configuration interaction (MNDO-PSDCI) molecular orbital theory calculation. The difference in the calculated absorption maxima between the cis and trans binding site models exhibits the same wavelength difference among the M/LWS opsins. The homology models of six M/LWS vertebrate opsins suggest that the more red-shifted pigments select a 6-s-trans ring conformation over a 6-s-cis conformation. Nomographic analysis indicates that selection of a 6-s-trans geometry red shifts the A1 pigments by ~1400 cm-1 and the A2 pigments by ~2700 cm-1. |
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Frontiers in Chemical Biology
5:00 PM-7:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Biological Chemistry |