ABSTRACT
Protein misfolding cyclic amplification (PMCA) is a highly sensitive technique used to detect minute amounts of scrapie prion protein (PrP(Sc)), a major protein component of the infectious agents associated with prion diseases. Although exponential in vitro amplification of hamster scrapie PrP(Sc) has been established, the PMCA used was unsuccessful in achieving good amplification of PrP(Sc) from other animals. Here, we have investigated the cause of the insufficient PrP(Sc) amplification in mice and have developed an improved method suitable for amplification of the PrP(Sc) of the mouse-adapted scrapie prion strain Chandler. Mouse PrP(C), the cellular form of the prion protein, tends to become resistant to proteases during incubation independent of sonication. By adding digitonin to the reaction buffer as a lipid detergent, accumulation of the protease-resistant PrP(C) was inhibited; hence, mouse PrP(Sc) could be amplified to infinite levels. The present study is the first report describing effective amplification of PrP(Sc) of the mouse-adapted scrapie prion and this improved PMCA technique will contribute to prion research that uses mice as experimental animals.
Subject(s)
PrPSc Proteins/metabolism , Prions/metabolism , Protein Folding , Animals , Mice , Mice, Inbred ICR , PrPSc Proteins/chemistry , Scrapie/metabolismABSTRACT
ADP-ribose pyrophosphatase (ADPRase) catalyzes the divalent metal ion-dependent hydrolysis of ADP-ribose to ribose 5'-phosphate and AMP. This enzyme plays a key role in regulating the intracellular ADP-ribose levels, and prevents nonenzymatic ADP-ribosylation. To elucidate the pyrophosphatase hydrolysis mechanism employed by this enzyme, structural changes occurring on binding of substrate, metal and product were investigated using crystal structures of ADPRase from an extreme thermophile, Thermus thermophilus HB8. Seven structures were determined, including that of the free enzyme, the Zn(2+)-bound enzyme, the binary complex with ADP-ribose, the ternary complexes with ADP-ribose and Zn(2+) or Gd(3+), and the product complexes with AMP and Mg(2+) or with ribose 5'-phosphate and Zn(2+). The structural and functional studies suggested that the ADP-ribose hydrolysis pathway consists of four reaction states: bound with metal (I), metal and substrate (II), metal and substrate in the transition state (III), and products (IV). In reaction state II, Glu-82 and Glu-70 abstract a proton from a water molecule. This water molecule is situated at an ideal position to carry out nucleophilic attack on the adenosyl phosphate, as it is 3.6 A away from the target phosphorus and almost in line with the scissile bond.
Subject(s)
Pyrophosphatases/chemistry , Thermus thermophilus/enzymology , Adenosine Diphosphate Ribose/chemistry , Amino Acid Motifs , Amino Acid Sequence , Binding Sites , Catalysis , Crystallography, X-Ray , Dimerization , Hydrolysis , Kinetics , Models, Molecular , Molecular Sequence Data , Mutation , Protein Binding , Protein Conformation , Protein Structure, Tertiary , Sequence Homology, Amino Acid , Zinc/chemistryABSTRACT
An ADP-ribose pyrophosphatase from Thermus thermophilus HB8 was overproduced in Escherichia coli and purified. Gel-filtration chromatography showed the protein to be in a dimeric state. This protein catalyses the Mg(2+)- or Zn(2+)-dependent hydrolysis of ADP-ribose to AMP and ribose-5'-phosphate. It was crystallized in the absence and the presence of ADP-ribose by the hanging-drop vapour-diffusion method. Complete data sets were collected to 1.50 A resolution from the apo form using synchrotron radiation and to 2.0 A resolution from the complexed form. Both crystals belong to space group P3(1)21 or P3(2)21 and contain one molecule in the asymmetric unit.
