title: Low-barrier hydrogen bond in photoactive yellow protein.
abstract: Low-barrier hydrogen bonds (LBHBs) have been proposed to play roles in protein functions, including enzymatic catalysis and proton transfer. Transient formation of LBHBs is expected to stabilize specific reaction intermediates. However, based on experimental results and theoretical considerations, arguments against the importance of LBHB in proteins have been raised. The discrepancy is caused by the absence of direct identification of the hydrogen atom position. Here, we show by high-resolution neutron crystallography of photoactive yellow protein (PYP) that a LBHB exists in a protein, even in the ground state. We identified approximately 87% (819/942) of the hydrogen positions in PYP and demonstrated that the hydrogen bond between the chromophore and E46 is a LBHB. This LBHB stabilizes an isolated electric charge buried in the hydrophobic environment of the protein interior. We propose that in the excited state the fast relaxation of the LBHB into a normal hydrogen bond is the trigger for photo-signal propagation to the protein moiety. These results give insights into the novel roles of LBHBs and the mechanism of the formation of LBHBs.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Hironari
authors.initials: H
authors.lastname: Kamikubo
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kurihara
authors.forename: Ryota
authors.initials: R
authors.lastname: Kuroki
authors.forename: Nobuo
authors.initials: N
authors.lastname: Niimura
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Shimizu
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Mikio
authors.initials: M
authors.lastname: Kataoka
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D033363:Neutron Diffraction; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria