title: The 2.5 A structure of pokeweed antiviral protein.
abstract: The pokeweed antiviral protein (PAP), isolated from the leaves of Phytolacca americana, is one of a family of plant and bacterial ribosome-inhibiting proteins (RIPs) which act as specific N-glycosidases on rRNA. Here we report the three-dimensional structure of PAP determined to 2.5 A resolution by X-ray crystallography. After 14 rounds of refinement, the R factor is 0.17 for 5.0 to 2.5 A data. The protein is homologous with the A chain of ricin and exhibits a very similar folding pattern. The positions of key active site residues are also similar. We also report the 2.8 A structure of PAP complexed with a substrate analog, formycin 5'-monophosphate. As seen previously in ricin, the formycin ring is stacked between invariant tyrosines 72 and 123. Arg179 bonds to N-3 which is thought to be important in catalysis.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas, Austin 78712.
authors.forename: A F
authors.initials: AF
authors.lastname: Monzingo
authors.forename: E J
authors.initials: EJ
authors.lastname: Collins
authors.forename: S R
authors.initials: SR
authors.lastname: Ernst
authors.forename: J D
authors.initials: JD
authors.lastname: Irvin
authors.forename: J D
authors.initials: JD
authors.lastname: Robertus
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D005573:Formycins / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D012265:Ribonucleotides / Q000737:chemistry; D054789:Ribosome Inactivating Proteins, Type 1; D012276:Ricin / Q000737:chemistry
chemical_list: D005573:Formycins; D010940:Plant Proteins; D012265:Ribonucleotides; D054789:Ribosome Inactivating Proteins, Type 1; C021683:formycin 5'-phosphate; D012276:Ricin; D009699:N-Glycosyl Hydrolases; C024275:pokeweed antiviral protein