title: Infrared spectral marker bands characterizing a transient water wire inside a hydrophobic membrane protein.
abstract: Proton conduction along protein-bound "water wires" is an essential feature in membrane proteins. Here, we analyze in detail a transient water wire, which conducts protons via a hydrophobic barrier within a membrane protein to create a proton gradient. It is formed only for a millisecond out of three water molecules distributed at inactive positions in a polar environment in the ground state. The movement into a hydrophobic environment causes characteristic shifts of the water bands reflecting their different chemical properties. These band shifts are identified by time-resolved Fourier Transform Infrared difference spectroscopy and analyzed by biomolecular Quantum Mechanical/Molecular Mechanical simulations. A non-hydrogen bonded ("dangling") O-H stretching vibration band and a broad continuum absorbance caused by a combined vibration along the water wire are identified as characteristic marker bands of such water wires in a hydrophobic environment. The results provide a basic understanding of water wires in hydrophobic environments.
authors.affiliation: Department of Biophysics, Ruhr-University Bochum, Universitätsstraße 150, 44780 Bochum, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Wolf
authors.affiliation: Department of Biophysics, Chinese Academy of Sciences, Max-Planck-Gesellschaft Partner Institute for Computational Biology, 320 Yue Yang Road, 200031 Shanghai, China.
authors.forename: Erik
authors.initials: E
authors.lastname: Freier
authors.affiliation: Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin, Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Cui
authors.affiliation: Department of Biophysics, Ruhr-University Bochum, Universitätsstraße 150, 44780 Bochum, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Gerwert
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D019617:Halobacterium salinarum / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water; D001436:Bacteriorhodopsins