title: Preparation of large crystals of photoactive yellow protein for neutron diffraction and high resolution crystal structure analysis.
abstract: The exact positions of all the hydrogen atoms in photoactive yellow protein (PYP) is important for understanding the molecular mechanism of the photoreaction because the protonation/deprotonation of certain amino acid residues and rearrangements in the hydrogen bond network are involved in the conformational changes of PYP. Neutron crystallography is one of the most effective methods to determine the hydrogen positions. However, a large crystal is required for neutron crystallography because a neutron-incident flux is quite limited. In addition, the crystal should be grown from heavy water to reduce the incoherent background from hydrogen. We prepared a large crystal of PYP (dimensions: 1.5 x 0.7 x 0.7 mm3) for neutron crystallography using ammonium sulfate with sodium chloride. The obtained large crystal gave X-ray diffraction spots up to 0.84 angstroms. Although some of the hydrogen atoms could be observed in the high resolution X-ray crystal structure, functionally important hydrogen atoms were impossible to see, indicating the importance of neutron crystallography. Thus, we optimized the crystallization conditions with heavy water and successfully obtained neutron diffraction spots up to 2.1 angstroms with the crystal in D2O.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Hironari
authors.initials: H
authors.lastname: Kamikubo
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Shimizu
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imamoto
authors.forename: Mikio
authors.initials: M
authors.lastname: Kataoka
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000528:radiation effects; D003460:Crystallization; D018360:Crystallography, X-Ray; D020607:Halorhodospira halophila / Q000737:chemistry / Q000528:radiation effects; D033363:Neutron Diffraction; D010777:Photochemistry; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000302:isolation & purification* / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria