Sensory rhodopsin I: receptor activation and signal relay.
Recent progress is summarized on the mechanism of phototransduction by sensory rhodopsin I (SR-I), a phototaxis receptor in Halobacterium halobium. Two aspects are emphasized: (i) The coupling of retinal isomerization to protein conformational changes. Retinal analogs have been used to probe chromophore-apoprotein interactions during the receptor activation process. One of the most important results is the finding of a steric trigger deriving from the interaction of residues on the protein with a methyl group near the isomerizing bond of the retinal (at carbon 13). Recent work on molecular genetic methods to further probe structure/function includes the synthesis and expression of an SR-I apoprotein gene designed for residue replacements by cassette mutagenesis, and transformation of an H. halobium mutant lacking all retinylidene proteins known in this species to SR-I+ and bacteriorhodopsin (BR)+. (ii) The relay of the SR-I signal to a post-receptor component. A carboxylmethylated protein ("MPP-I") associated with SR-I and found in the H. halobium membrane exhibits homology with the signaling domain of eubacterial chemotaxis transducers (e.g., Escherichia coli Tar, Tsr, and Trg proteins), suggesting a model based on SR-I----MPP-I signal relay.
Spudich
J L
JL
Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston 77030.
Bogomolni
R A
RA
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000378:metabolism*; D019617:Halobacterium salinarum / Q000378:metabolism; D025602:Halorhodopsins; D008565:Membrane Proteins / Q000378:metabolism; D000072236:Methyl-Accepting Chemotaxis Proteins; D008969:Molecular Sequence Data; D010777:Photochemistry; D011487:Protein Conformation; D025603:Sensory Rhodopsins; D015398:Signal Transduction
D001426:Bacterial Proteins; D025602:Halorhodopsins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; C061497:SRI protein, Halobacterium; D025603:Sensory Rhodopsins; C000607604:tsr protein, E coli; D001436:Bacteriorhodopsins