Multicolored protein conformation states in the photocycle of transducer-free sensory rhodopsin-I

ABSTRACT Sensory rhodopsin-I (SRI), a phototaxis receptor of archaebacteria, is a retinal-binding protein that exists in the cell membrane intimately associated with a signal-transducing protein (Htrl) homologous to eubacterial chemotaxis receptors. Transducer-free sensory rhodopsin-I (fSRI), from cells devoid of Htrl, undergoes a photochemical cycle kinetically different from that of native SRI. We report here on the measurement and analysis of the photochemical kinetics of fSRI reactions in the 350-750-nm spectral range and in a 10-7 s to 1 s time window. The lack of specific intermolecular interactions between SRI and Htrl results in early return of the ground form via distinct …