title: Crystal structure of chloroplastic ascorbate peroxidase from tobacco plants and structural insights into its instability.
abstract: Ascorbate peroxidase (APX) is a heme-containing protein that plays a central role in scavenging H(2)O(2) in higher plants. The structure of stromal APX (sAPX) was determined at 1.6 A to an R-factor of 19.1% and an R-free-factor of 22.3%. The electrostatic potential of the gamma-channel that connects the molecular surface of sAPX to the gamma-edge of heme was more positive than that of cytosolic APX (cAPX) from pea, so sAPX might bind more easily with ascorbate than cAPX. The overall structure of sAPX was similar to those of cAPX from pea and cytochrome c peroxidase (CCP) from yeast, with a substantial difference in a loop structure located in the vicinity of the heme. The side chain of Arg169 in sAPX corresponding to His169 in cAPX and His181 in CCP extended in the opposite direction from the heme, forming two hydrogen bonds with carbonyl groups in the loop structure. The rapid inactivation of sAPX might be due to the characteristic conformation of Arg169 owing to the loop structure of sAPX.
authors.affiliation: Research Institute for Advanced Science and Technology, Osaka Prefecture University, Gakuen-cho 1-2, Sakai, Osaka 599-8570.
authors.forename: Kei
authors.initials: K
authors.lastname: Wada
authors.forename: Toshiji
authors.initials: T
authors.lastname: Tada
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Yabuta
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yoshimura
authors.forename: Shigeru
authors.initials: S
authors.lastname: Shigeoka
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Nishimura
mesh_terms: D060387:Ascorbate Peroxidases; D001665:Binding Sites; D002736:Chloroplasts / Q000201:enzymology*; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D007527:Isoenzymes; D008958:Models, Molecular; D018532:Pisum sativum / Q000201:enzymology; D010544:Peroxidases / Q000737:chemistry*; D017433:Protein Structure, Secondary; D055672:Static Electricity; D014026:Nicotiana / Q000201:enzymology*; D015003:Yeasts / Q000201:enzymology
chemical_list: D007527:Isoenzymes; D010544:Peroxidases; D060387:Ascorbate Peroxidases