title: The signal transfer from the receptor NpSRII to the transducer NpHtrII is not hampered by the D75N mutation.
abstract: Sensory rhodopsin II (NpSRII) is a phototaxis receptor of Natronomonas pharaonis that performs its function in complex with its cognate transducer (NpHtrII). Upon light activation NpSRII triggers by means of NpHtrII a signal transduction chain homologous to the two component system in eubacterial chemotaxis. The D75N mutant of NpSRII, which lacks the blue-shifted M intermediate and therefore exhibits a significantly faster photocycle compared to the wild-type, mediates normal phototaxis responses demonstrating that deprotonation of the Schiff base is not a prerequisite for transducer activation. Using site-directed spin labeling and time resolved electron paramagnetic-resonance spectroscopy, we show that the mechanism revealed for activation of the wild-type complex, namely an outward tilt motion of the cytoplasmic part of the receptor helix F and a concomitant rotation of the transmembrane transducer helix TM2, is also valid for the D75N variant. Apparently, the D75N mutation shifts the ground state conformation of NpSRII-D75N and its cognate transducer into the direction of the signaling state.
authors.affiliation: Fachbereich Physik, Universität Osnabrück, Osnabrück, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Holterhues
authors.forename: Enrica
authors.initials: E
authors.lastname: Bordignon
authors.forename: Daniel
authors.initials: D
authors.lastname: Klose
authors.forename: Christian
authors.initials: C
authors.lastname: Rickert
authors.forename: Johann P
authors.initials: JP
authors.lastname: Klare
authors.forename: Swetlana
authors.initials: S
authors.lastname: Martell
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Martin
authors.initials: M
authors.lastname: Engelhard
authors.forename: Heinz-Jürgen
authors.initials: HJ
authors.lastname: Steinhoff
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D019633:Natronobacterium / Q000378:metabolism* / Q000528:radiation effects; D017433:Protein Structure, Secondary; D015398:Signal Transduction / Q000528:radiation effects; D013113:Spin Labels; D013997:Time Factors
chemical_list: D019843:Archaeal Proteins; C434451:HtrII protein, Natronobacterium pharaonis; D050505:Mutant Proteins; D013113:Spin Labels; C434450:phototaxis receptor sensory rhodopsin II, Natronobacterium pharaonis; D002338:Carotenoids