Abstract
Bacteriorhodopsin is a light-driven hydrogen-ion pump whose structure is known to about 6.0 Å in three dimensions and 2.8 Å in projection. It consists of seven transmembrane helices surrounding the chromophore, retinal. Halorhodopsin is a second member of the same family of membrane proteins, both of them from the cell membrane of halobacteria. Halorhodopsin is a light-driven chloride-ion pump but has very close homology to bacteriorhodopsin, especially around the retinal. In contrast, the visual opsins that are responsible for the primary step in visual transduction in all eukaryotes from
Drosophila
upwards, form a separate family with no direct sequence homology to the bacteriorhodopsin family. The visual opsin family now includes about 15 other receptor proteins, all of which activate G-protein cascades, including the β-adrenergic receptor as well as several others. Despite the lack of clear relations at the level of amino acid sequence, there are topographical similarities between the bacteriorhodopsin and the visual opsin families in the nature and site of chromophore attachment, the number of transmembrane helices and the positions of the amino and carboxyl termini in the membrane. These suggest that if the two were at one time closely related, they have diverged too far to have sequences that are detectably similar.
Subject
Industrial and Manufacturing Engineering,General Agricultural and Biological Sciences,General Business, Management and Accounting,Materials Science (miscellaneous),Business and International Management
Cited by
110 articles.
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