title: Structural dynamics of water and the peptide backbone around the Schiff base associated with the light-activated process of octopus rhodopsin.
abstract: Difference Fourier transform infrared spectra were recorded for the formation of the photointermediates and isorhodopsin from octopus rhodopsin at low temperatures. Analysis was done for H bonding of the Schiff base, internal water molecules, and the peptide backbone. The imine hydrogen of the Schiff base was in the same H bonding state throughout the photointermediates and the unphotolyzed state. In contrast, H bonding of the hydrogen of the water molecule whose oxygen might be complexed with the imine hydrogen of the Schiff base was altered upon the formation of bathorhodopsin. The same water molecule was in a different H bonding state in the subsequent intermediates, lumirhodopsin and mesorhodopsin. These intermediates were also characterized by a decrease in the C = N bond order of the Schiff base as a reflection of distorted structure around the Schiff base. The polar N-H bond in these intermediates could be also ascribed to the Schiff base. Some changes in H bonding of water and the perturbation of the polyene chain in lumirhodopsin and mesorhodopsin were also observed in isorhodopsin. Acid metarhodopsin exhibited extensive changes in the H bonding states of the peptide backbone and internal water molecules. A large part of these changes was extinguished in alkaline metarhodopsin with the unprotonated Schiff base, suggesting interaction of the protonated Schiff base with the peptide backbone and intramembrane water molecules in acid metarhodopsin.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nishimura
authors.forename: H
authors.initials: H
authors.lastname: Kandori
authors.forename: M
authors.initials: M
authors.lastname: Nakagawa
authors.forename: M
authors.initials: M
authors.lastname: Tsuda
authors.forename: A
authors.initials: A
authors.lastname: Maeda
mesh_terms: D000818:Animals; D002417:Cattle; D006860:Hydrogen Bonding; D066298:In Vitro Techniques; D015394:Molecular Structure; D049831:Octopodiformes; D010455:Peptides / Q000737:chemistry; D010777:Photochemistry; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000528:radiation effects*; D012545:Schiff Bases / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D010455:Peptides; D012545:Schiff Bases; D014867:Water; C013110:metarhodopsins; D012243:Rhodopsin