 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 8]](be5237fig8mag.jpg)
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Figure 8
Comparison of B–C interhelical segments in proteorhodopsin, bacteriorhodopsin and xanthorhodopsin. (a) Superposition of the BR protomer (gray; PDB entry 1c3w ; Luecke et al., 1999  ) onto Med12BPR protomer A (blue; r.m.s.d. = 1.48 Å). The B–C interhelical segment of each protein is circled. BR has an antiparallel β-sheet which shields the proton-release region from the extracellular side, while BPR has a relatively short loop that leaves this region exposed. (b) Superposition of the XR protomer (light orange; PDB entry 3ddl
; Luecke et al., 2008) onto Med12BPR protomer A (blue; r.m.s.d. = 1.98 Å). The B–C interhelical segment of XR also consists of an antiparallel β-sheet, as in BR, but this region is flipped towards the N-terminus, resulting in a large cavity near the proton-release group. A similar cavity exists in BPR but to a lesser degree because the displacement of the B–C and F–G interhelical segments is not as large. (c) Space-filling model of Med12BPR protomer A with the seven helices highlighted. The putative proton-release group of Glu142(124), Tyr95(77), Tyr208(191) and Tyr223(205) is displayed as a space-filling model colored yellow. This region has direct access to the extracellular side because it is not blocked by an extended B–C interhelical segment. The figures were generated with PyMOL. |
![[Figure 8]](be5237fig8.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
