Retinal location in purple membrane of Halobacterium halobium: a neutron diffraction study of membranes labelled in vivo with deuterated retinal
Jubb, J.S.; Worcester, D.L.; Crespi, H.L.; Zaccaï, G.
EMBO Journal 3(7): 1455-1461
1984
ISSN/ISBN: 0261-4189 PMID: 6745237 Document Number: 238188
Purple membranes were prepared by growing H. halobium in a medium containing nicotine (which inhibits biosynthesis of retinal) and the oxidation products of fully deuterated .beta.-carotene. This allowed the in vivo incorporation of deuterated retinal into the membranes. The labeled membranes were crystalline and isomorphous with native membrane, as determined by X-ray diffraction, and their optical absorption spectra were very similar. Neutron diffraction data for the 2-dimensional in-plane lattice from labeled and native membranes were analyzed by difference Fourier and direct methods to 8.6 .ANG. resolution. The difference Fourier shows the retinal to be located in the center of the bacteriorhodopsin molecule. The best fit to the data was obtained with the projection of retinal as a 10 .ANG. long rod forming an angle of -40.degree. .+-. 10.degree. with the x axis centered at x = -0.19 .+-. 0.02, y = -0.35 .+-. 0.02 in fractional unit cell coordinates. The main peak in the difference Fourier map is at x = -0.17, y = -0.33.