title: Complex formation and light activation in membrane-embedded sensory rhodopsin II as seen by solid-state NMR spectroscopy.
abstract: Microbial rhodopsins execute diverse biological functions in the cellular membrane. A mechanistic understanding of their functional profile is, however, still limited. We used solid-state NMR (ssNMR) spectroscopy to study structure and dynamics of a 2 x 400 amino acid sensory rhodopsin/transducer (SRII/HtrII) complex from Natronomonas pharaonis in a natural membrane environment. We found a receptor-transducer binding interface in the ground state that significantly extends beyond the available X-ray structure. This binding domain involves the EF loop of the receptor and stabilizes the functionally relevant, directly adjacent HAMP domain of the transducer. Using 2D ssNMR difference spectroscopy, we identified protein residues that may act as a functional module around the retinal binding site during the early events of protein activation. These latter protein segments, the inherent plasticity of the HAMP domain, and the observation of an extended SRII/HtrII membrane-embedded interface may be crucial components for optimal signal relay efficiency across the cell membrane.
authors.affiliation: Department for NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Etzkorn
authors.forename: Karsten
authors.initials: K
authors.lastname: Seidel
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Swetlana
authors.initials: S
authors.lastname: Martell
authors.forename: Matthias
authors.initials: M
authors.lastname: Geyer
authors.forename: Martin
authors.initials: M
authors.lastname: Engelhard
authors.forename: Marc
authors.initials: M
authors.lastname: Baldus
mesh_terms: D000595:Amino Acid Sequence; D025602:Halorhodopsins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D019633:Natronobacterium / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D025603:Sensory Rhodopsins / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal