Met-145 is a key residue in the dark adaptation of bacteriorhodopsin homologs.
Composition of retinal isomers in three proton pumps (bacteriorhodopsin, archaerhodopsin-1, and archaerhodopsin-2) was determined by high performance liquid chromatography in their light-adapted and dark-adapted states. In the light-adapted state, more than 95% of the retinal in all three proton pumps were in the all-trans configuration. In the dark-adapted state, there were only two retinal isomers, all-trans and 13-cis, in the ratio of all-trans: 13-cis = 1:2 for bacteriorhodopsin, 1:1 for archaerhodopsin-1, and 3:1 for archaerhodopsin-2. The difference in the final isomer ratios in the dark-adapted bacteriorhodopsin and archaerhodopsin-2 was ascribed to the methionine-145 in bacteriorhodopsin. This is the only amino acid in the retinal pocket that is substituted by phenylalanine in archaerhodopsin-2. The bacteriorhodopsin point-mutated at this position to phenylalanine dramatically altered the final isomer ratio from 1:2 to 3:1 in the dark-adapted state. This point mutation also caused a 10 nm blue-shift of the adsorption spectrum, which is similar to the shift of archaerhodopsin-2 relative to the spectra of bacteriorhodopsin and archaerhodopsin-1.
Ihara
K
K
Department of Biology, School of Science, Nagoya University, Japan.
Amemiya
T
T
Miyashita
Y
Y
Mukohata
Y
Y
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D019843:Archaeal Proteins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D001483:Base Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D004247:DNA / Q000235:genetics; D003624:Darkness; D019617:Halobacterium salinarum / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D008969:Molecular Sequence Data; D010777:Photochemistry; D017354:Point Mutation; D012172:Retinaldehyde / Q000737:chemistry / Q000528:radiation effects; D013053:Spectrophotometry; D013237:Stereoisomerism; D013696:Temperature; D017494:Proton Pumps
D019843:Archaeal Proteins; D001426:Bacterial Proteins; D001436:Bacteriorhodopsins; D004247:DNA; D012172:Retinaldehyde; C055476:archaerhodopsin protein, Archaea; D017494:Proton Pumps