title: H atom positions and nuclear magnetic resonance chemical shifts of short H bonds in photoactive yellow protein.
abstract: Recent neutron diffraction studies on photoactive yellow protein (PYP) proposed that the H bond between protonated Glu46 and the chromophore-ionized p-coumaric acid (pCA) is a low-barrier H bond (LBHB) mainly because the H atom position was assigned at the midpoint of the O(Glu46)-O(pCA) bond. However, the (1)H nuclear magnetic resonance (NMR) chemical shift (δ(H)) was 15.2 ppm, which is lower than the values of 17-19 ppm for typical LBHBs. We evaluated the dependence of δ(H) on an H atom position in the O(Glu46)-O(pCA) bond in the PYP ground state by using a quantum mechanical/molecular mechanical (QM/MM) approach. The calculated chemical shift unambiguously suggested that a δ(H) of 15.2 ppm for the O(Glu46)-O(pCA) bond in NMR studies should correspond to the QM/MM geometry (δ(H) = 14.5 ppm), where the H atom belongs to the Glu moiety, rather than the neutron diffraction geometry (δ(H) = 19.7 ppm), where the H atom is near the midpoint of the donor and acceptor atoms.
authors.affiliation: Career-Path Promotion Unit for Young Life Scientists, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Saito
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikita
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D020607:Halorhodospira halophila / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D033363:Neutron Diffraction; D019906:Nuclear Magnetic Resonance, Biomolecular; D020283:Photoreceptors, Microbial / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria; D006859:Hydrogen