Figure 9.

Hydrogen bonds involving side chains of Glu122 and His211. Fragments of rhodopsin helices 3 (red), 4 (orange) and 5 (yellow) are shown in relationship to the retinylidene chromophore (green). Shown by dotted lines are hydrogen bonds proposed to exist from Glu122 to the backbone carbonyl of His211 (2.8 Å) and to the side chain of Trp126 (3.1 Å). Also shown by a dotted line is the proposed rhodopsin hydrogen bond from the side chain of His211 to the hydroxyl of Tyr206 (2.9 Å). The distance from the hydroxyl of Tyr206 to the non-helical backbone carbonyl of Ala166 (2.6 Å) is shown by a solid line. Note that if His211 is unprotonated, Tyr206 can participate in only one of these potential hydrogen bonds. Also of interest is that the distance from His211 to Trp126 (3.3 Å) is only slightly greater than from Glu122. The coordinates used to generate this view were derived from molecule A of Li 3 et al. (5).