DIFFERENT MODES OF PROTON TRANSLOCATION BY SENSORY RHODOPSIN-I

The membrane-bound complex between sensory rhodopsin I (SRI) and its t ransducer HtrI forms the functional photoreceptor unit that allows tra nsmission of light signals to the flagellar motor, although being a ph otosensor, SRI, the mutant SRI-D76N and the HtrI-SRI complex can trans port protons, as we demonstrate by using the sensitive and ion-specifi c black lipid membrane technique, SRI sustains an orange light-driven (one-photon-driven) outward proton transport which is enhanced by addi tional blue light (two-photon-driven). The vectoriality of the two-pho ton-driven transport could be reversed at neutral pH from the outward to the inward direction by switching the cutoff wavelength of the long wavelength light from 550 to 630 mn, The cvt-off wavelength determini ng the reversal point decreases with decreasing pH. The currents could be enhanced by azide. A two-photon-driven inward proton transport by SRI-D76N (catalyzed by azide) and by the complex HtrI-SRI is demonstra ted. The influence of pH and azide concentration on the rise and decay kinetics of the SRI(380) intermediate is analyzed. The different mode s of proton translocation of the SRI species are discussed on the basi s of a general model of proton translocation of retinal proteins and i n the context of signal transduction.