Tham khảo tài liệu 'atomic force microscopy in cell biology episode 2 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 266 Muller and Engel Fig. 5 Imaging a polypeptide loop grafted onto bacteriorhodopsin. A Secondary structural model of bacteriorhodopsin from Halobacterium salinarum. B The polypeptide loop connecting transmembrane a-helices E and F loop EF of the bacteriorhodopsin molecule was replaced by loop EF from bovine rhodopsin to produce the mutant IIIN indicated by the filled circles the numbering in the boxes give the residue in IIIN first and the residue in the rhodopsin loop second . V8 protease cleaves this loop after the glutamates indicated by the arrows see Fig. 6 . C Topograph of the mutant IIIN containing the rhodopsin EF loop. D Threefold symmetrized correlation average of mutant IIIN trimer. E Standard deviation map of the average. F Threefold symmetrized correlation average of the bacteriorhodopsin trimer imaged elsewhere Muller Sass et al. 1999 . G Standard deviation map of the bacteriorhodopsin trimer. The outlined BR monomer represents a section close to the cytoplasmic surface of the lipid membrane and the positions of the transmembrane a-helices A to F were obtained after merging six atomic models of BR Heymann et al. 1999 . Vertical brightness range of contact mode topographs corresponds to nm. Minima and maxima of the SD maps were and nm for E and and nm for G respectively. 13. Atomic Force Microscopy and Spectroscopy of Membrane Proteins 267 rhodopsin Rho EF also interacts with rhodopsin kinase which phosphorylates light-activated rhodopsin and with arrestin which displaces transducin from light-activated phosphorylated rhodopsin. To directly observe the rhodopsin loop purple membrane containing the mutant bacteriorhodopsin called IIIN was imaged by AFM under physiological conditions to a resolution of nm Fig. 5C . It was found that the modification of loop EF changed neither the crystallographic lattice nor the extracellular surface Heymann et al. 2000 . This was notunexpected because fragments ofbacteriorhodopsin separated
