Probing the sensory rhodopsin II binding domain of its cognate transducer by calorimetry and electrophysiology.

Sensory rhodopsin II, a repellent phototaxis receptor from Natronobacterium pharaonis (NpSRII) forms a tight complex with its cognate transducer (NpHtrII). Light excitation of the receptor triggers conformational changes in both proteins, thereby activating the cellular two-component signalling cascade. In membranes, the two proteins form a 2:2 complex, which dissociates to a 1:1 heterodimer in micelles.

Electric-field dependent decays of two spectroscopically different M-states of photosensory rhodopsin II from Natronobacterium pharaonis.

Sensory rhodopsin II (NpSRII) from Natronobacterium pharaonis was studied by resonance Raman (RR) spectroscopic techniques. Using gated 413-nm excitation, time-resolved RR measurements of the solubilized photoreceptor were carried out to probe the photocycle intermediates that are formed in the submillisecond time range. For the first time, two M-like intermediates were identified on the basis of their C=C stretching bands at 1568 and 1583 cm(-1), corresponding to the early M(L)(400) state with a lifetime of 30 micro s and the subsequent M(1)(400) state with a lifetime of 2 ms, respectively.