The photochemical reactions of sensory rhodopsin I are altered by its transducer.
The sopI gene, which encodes the phototaxis receptor sensory rhodopsin I (SR-I), was expressed in Halobacterium salinarium strains with chromosomal deletions of (i) sopI only or of (ii) the region containing sopI and htrI. The htrI gene encodes a transducer protein for SR-I signals. Transformation of the sopI deletion mutant containing the htrI gene by a multicopy expression plasmid for sopI results in normal physiological and photochemical properties of SR-I. Transformation by the same plasmid of the mutant lacking the htrI gene as well as sopI results in production of pigment with a normal absorption spectrum but altered photochemical properties, and no phototaxis by the transformants. Analysis of flash-induced absorbance changes shows that the transducer protein increases light-induced production of the photocycle intermediate S373, the SR-I signaling conformation, and modulates the rate of S373 return to the prestimulus state, rendering this return pH-independent. These effects are interpreted in terms of receptor/transducer interactions that influence proton transfer reactions occurring in the photoactive site.
Spudich
E N
EN
Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston 77030.
Spudich
J L
JL
D019843:Archaeal Proteins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001436:Bacteriorhodopsins / Q000235:genetics / Q000378:metabolism*; D006217:Halobacterium / Q000235:genetics / Q000378:metabolism*; D025602:Halorhodopsins; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D025603:Sensory Rhodopsins; D014161:Transduction, Genetic
D019843:Archaeal Proteins; D001426:Bacterial Proteins; D025602:Halorhodopsins; D008565:Membrane Proteins; C061497:SRI protein, Halobacterium; D025603:Sensory Rhodopsins; C082504:htrI protein, Halobacterium salinarium; D001436:Bacteriorhodopsins