title: Structure of grouper iridovirus purine nucleoside phosphorylase.
abstract: Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of purine ribonucleosides to the corresponding free bases and ribose 1-phosphate. The crystal structure of grouper iridovirus PNP (givPNP), corresponding to the first PNP gene to be found in a virus, was determined at 2.4 A resolution. The crystals belonged to space group R3, with unit-cell parameters a = 193.0, c = 105.6 A, and contained four protomers per asymmetric unit. The overall structure of givPNP shows high similarity to mammalian PNPs, having an alpha/beta structure with a nine-stranded mixed beta-barrel flanked by a total of nine alpha-helices. The predicted phosphate-binding and ribose-binding sites are occupied by a phosphate ion and a Tris molecule, respectively. The geometrical arrangement and hydrogen-bonding patterns of the phosphate-binding site are similar to those found in the human and bovine PNP structures. The enzymatic activity assay of givPNP on various substrates revealed that givPNP can only accept 6-oxopurine nucleosides as substrates, which is also suggested by its amino-acid composition and active-site architecture. All these results suggest that givPNP is a homologue of mammalian PNPs in terms of amino-acid sequence, molecular mass, substrate specificity and overall structure, as well as in the composition of the active site.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
authors.forename: You-Na
authors.initials: YN
authors.lastname: Kang
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Paula W
authors.initials: PW
authors.lastname: Allan
authors.forename: William B
authors.initials: WB
authors.lastname: Parker
authors.forename: Jing-Wen
authors.initials: JW
authors.lastname: Ting
authors.forename: Chi-Yao
authors.initials: CY
authors.lastname: Chang
authors.forename: Steven E
authors.initials: SE
authors.lastname: Ealick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017995:Ranavirus / Q000201:enzymology* / Q000235:genetics; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D010710:Phosphates; D011683:Purine-Nucleoside Phosphorylase