title: Crystal structure of orotate phosphoribosyltransferase.
abstract: Phosphoribosyltransferases (PRTases) are enzymes involved in the synthesis of purine, pyrimidine, and pyridine nucleotides. They utilize alpha-D-5-phosphoribosyl-1-pyrophosphate (PRPP) and a nitrogenous base to form a beta-N-riboside monophosphate and pyrophosphate (PPi), and their functional significance in nucleotide homeostasis is evidenced by the devastating effects of inherited diseases associated with the decreased activity and/or stability of these enzymes. The 2.6-A structure of the Salmonella typhimurium orotate phosphoribosyltransferase (OPRTase) complexed with its product orotidine monophosphate (OMP) provides the first detailed image of a member of this group of enzymes. The OPRTase three-dimensional structure was solved using multiple isomorphous replacement methods and reveals two major features: a core five-stranded alpha/beta twisted sheet and an N-terminal region that partially covers the C-terminal portion of the core. PRTases show a very high degree of base specificity. In OPRTase, this is determined by steric constraints and the position of hydrogen bond donors/acceptors of a solvent-inaccessible crevice where the orotate ring of bound OMP resides. Crystalline OPRTase is a dimer, with catalytically important residues from each subunit available to the neighboring subunit, suggesting that oligomerization is necessary for its activity. On the basis of the presence of a common PRPP binding motif among PRTases and the similar chemistry these enzymes perform, we propose that the alpha/beta core found in OPRTase will represent a common feature for PRTases. This generality is demonstrated by construction of a model of the human hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) from secondary structure predictions for HGPRTase and the three-dimensional structure of OPRTase.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: G
authors.initials: G
authors.lastname: Scapin
authors.forename: C
authors.initials: C
authors.lastname: Grubmeyer
authors.forename: J C
authors.initials: JC
authors.lastname: Sacchettini
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006860:Hydrogen Bonding; D007041:Hypoxanthine Phosphoribosyltransferase / Q000737:chemistry; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009711:Nucleotides / Q000378:metabolism; D009962:Orotate Phosphoribosyltransferase / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary
chemical_list: D046911:Macromolecular Substances; D009711:Nucleotides; D009962:Orotate Phosphoribosyltransferase; D007041:Hypoxanthine Phosphoribosyltransferase