Sensory rhodopsin II

Sensory rhodopsin II (SRII), also known as pharaonis phoborhodopsin (ppR), is a membrane protein of archaea, responsible generating the phototaxis signal.

Sensory rhodopsin II is found in Halobacterium salinarum and Natronomonas pharaonis.

Notable feature of sensory rhodopsin II is presence of charged residue Y199 on the surface of the hydrophobic region.

This residue is responsible for binding of sensory rhodopsin II transducer protein - HtrII.

In case of Halobacterium salinarum HtrII also comprises extracellular chemosensor region, which is responsible for serine sensing.

Crystal structure of NpSRII-HtrII complex dimer. SRII is in blue. View is along the membrane, extracellular space is on the top. Only transmembrane helices of HtrII are resolved.