Projection structure of frog rhodopsin in two crystal forms.
Rhodopsin is the G protein-coupled receptor that upon light activation triggers the visual transduction cascade. Rod cell outer segment disc membranes were isolated from dark-adapted frog retinas and were extracted with Tween detergents to obtain two-dimensional rhodopsin crystals for electron crystallography. When Tween 80 was used, tubular structures with a p2 lattice (a = 32 A, b = 83 A, gamma = 91 degrees) were formed. The use of a Tween 80/Tween 20 mixture favored the formation of larger p22(1)2(1) lattices (a = 40 A, b = 146 A, gamma = 90 degrees). Micrographs from frozen hydrated frog rhodopsin crystals were processed, and projection structures to 7-A resolution for the p22(1)2(1) form and to 6-A resolution for the p2 form were calculated. The maps of frog rhodopsin in both crystal forms are very similar to the 9-A map obtained previously for bovine rhodopsin and show that the arrangement of the helices is the same. In a tentative topographic model, helices 4, 6, and 7 are nearly perpendicular to the plane of the membrane. In the higher-resolution projection maps of frog rhodopsin, helix 5 looks more tilted than it appeared previously. The quality of the two frog rhodopsin crystals suggests that they would be suitable to obtain a three-dimensional structure in which all helices would be resolved.
Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom.
G F
GF
Schertler
P A
PA
Hargrave
D000818:Animals; D001001:Anura; D001436:Bacteriorhodopsins / Q000737:chemistry; D002417:Cattle; D003461:Crystallography; D004583:Electrons; D007091:Image Processing, Computer-Assisted; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012243:Rhodopsin / Q000737:chemistry*; D012374:Rod Cell Outer Segment / Q000737:chemistry; D013045:Species Specificity
D001436:Bacteriorhodopsins; D012243:Rhodopsin