A cytoplasmic domain is required for the functional interaction of SRI and HtrI in archaeal signal transduction.
Phototaxis in the archaeon Halobacterium salinarium is mediated by a stable complex of the photoreceptor sensory rhodopsin I and its transducer HtrI, which relays the light stimulus to the signalling pathway. Removal of the cytoplasmic signalling domain of HtrI eliminated the SRI-specific motor response to light stimulation and led to the loss of the spectroscopically detectable physical interaction of SRI and HtrI. A similar phenotype was obtained by deleting part of a cytoplasmic loop located between the second transmembrane helix of HtrI and the signalling domain. These results indicate that the photochemical behavior of sensory rhodopsin I is not determined by interaction with the transmembrane helices of HtrI per se but functionally coupled to the signalling domain. It is proposed that light excitation of SRI results in a conformational change of the transducer which is conducted by the cytoplasmic loop, an extra module not found in the eubacterial transducer homologues, and activates the signalling domain.
Max-Planck-Institut für Biochemie, Martinsried, Germany.
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Krah
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Marwan
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Oesterhelt
D019843:Archaeal Proteins; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D001436:Bacteriorhodopsins / Q000378:metabolism*; D001483:Base Sequence; D003593:Cytoplasm / Q000737:chemistry; D006217:Halobacterium / Q000502:physiology*; D025602:Halorhodopsins; D008027:Light; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D025603:Sensory Rhodopsins; D015398:Signal Transduction / Q000502:physiology* / Q000528:radiation effects
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