Archaebacterial photoreceptors mediate phototaxis by regulating cell motility through two-component signaling cascades like those found in chemotaxis signaling chains of enteric bacteria. The photoreceptor sensory rhodopsin II from N. pharaonis (NpSRII) in complex with its cognate transducer NpHtrII serves as a system for transmembrane signal transfer. This entry is for the transmembrane domain of the transducer HtrII. Studies suggest that conformation changes of the NpSRII/NpHtrII complex may be crucial for the mechanism of signal propagation spanning the membrane domain and feeding into the HAMP domain [1]. Furthermore, HtrII in H. salinarum not only transmits the signal from the photoreceptor SRII but also operates as a chemoreceptor [2].

1: New Insights on Signal Propagation by Sensory Rhodopsin II/Transducer Complex. Ishchenko A, Round E, Borshchevskiy V, Grudinin S, Gushchin I, Klare JP, Remeeva A, Polovinkin V, Utrobin P, Balandin T, Engelhard M, Buldt G, Gordeliy V; Sci Rep. 2017;7:41811. PMID:28165484

2: Ground state structure of D75N mutant of sensory rhodopsin II in complex with its cognate transducer. Ishchenko A, Round E, Borshchevskiy V, Grudinin S, Gushchin I, Klare JP, Balandin T, Remeeva A, Engelhard M, Buldt G, Gordeliy V; J Photochem Photobiol B. 2013;123:55-58. PMID:23619282