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Figure 2.
FIGURE 2. Crystal structure of squid rhodopsin. A,
schematic model of squid rhodopsin with multicolored cylindrical
helices. Transmembrane helices are indicated as TH1–TH7, and
amphipathic short helix H8 is indicated as H8. 11-cis-Retinal at
Lys-305 and palmitoylated cysteines Cys-336 and Cys-337 are
indicated by the yellow sphere-and-stick models. A hydrophilic
short helix in each N- and C-terminal tail is indicated as NH
and CH, respectively. N and C termini are indicated by the
letters N and C, and the cytoplasmic loop 3 is indicated as CL3.
Putative transmembrane-spanning regions are indicated by yellow
belts. B, superimposed schematic models and electrostatic
surfaces of known GPCR structures. Superimposed schematic
structures of squid and bovine rhodopsins, and β[2]AR are
shown. Squid rhodopsin in this study is shown in orange, bovine
rhodopsin in the trigonal crystal (1GZM) (17) is blue, and
β[2]AR (2RH1) excluding the T4 lysozyme part of CL3 (8) is sky
blue. The electrostatic surfaces of squid rhodopsin (Squ Rhod),
bovine rhodopsin in the trigonal crystal (Bov Rhod), and β[2]AR
(β2AR) are represented in blue (positive) to red (negative)
with the squid rhodopsin structure in an orange schematic. To
clarify the contribution of the distal C-terminal tail, the
electrostatic surface of squid rhodopsin without the C-terminal
tail after Glu-343 was also calculated (Squ C-trc). Different
TH5 regions are indicated by the red line.
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