Avian reovirus core protein muA expressed in Escherichia coli possesses both NTPase and RTPase activities.
Analysis of the amino acid sequence of core protein muA of avian reovirus has indicated that it may share similar functions to protein mu2 of mammalian reovirus. Since mu2 displayed both nucleotide triphosphatase (NTPase) and RNA triphosphatase (RTPase) activities, the purified recombinant muA ( muA) was designed and used to test these activities. muA was thus expressed in bacteria with a 4.5 kDa fusion peptide and six His tags at its N terminus. Results indicated that muA possessed NTPase activity that enabled the protein to hydrolyse the beta-gamma phosphoanhydride bond of all four NTPs, since NDPs were the only radiolabelled products observed. The substrate preference was ATP>CTP>GTP>UTP, based on the estimated k(cat) values. Alanine substitutions for lysines 408 and 412 (K408A/K412A) in a putative nucleotide-binding site of muA abolished NTPase activity, further suggesting that NTPase activity is attributable to protein muA. The activity of muA is dependent on the divalent cations Mg(2+) or Mn(2+), but not Ca(2+) or Zn(2+). Optimal NTPase activity of muA was achieved between pH 5.5 and 6.0. In addition, muA enzymic activity increased with temperature up to 40 degrees C and was almost totally inhibited at temperatures higher than 55 degrees C. Tests of phosphate release from RNA substrates with muA or K408A/K412A muA indicated that muA, but not K408A/K412A muA, displayed RTPase activity. The results suggested that both NTPase and RTPase activities of muA might be carried out at the same active site, and that protein muA could play important roles during viral RNA synthesis.
Su
Yu Pin
YP
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan.
Shien
Jui Huang
JH
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan.
Liu
Hung Jen
HJ
Department of Veterinary Medicine, National Pingtung University of Science and Technology, Pingtung 912, Taiwan.
Yin
Hsien Sheng
HS
Institute of Bioinformatics and Structural Biology, College of Life Sciences, National Tsing Hua University, Hsinchu 300, Taiwan.
Lee
Long Huw
LH
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan.
D017766:Acid Anhydride Hydrolases / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D001665:Binding Sites / Q000235:genetics; D003001:Cloning, Molecular; D003067:Coenzymes / Q000494:pharmacology; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008670:Metals / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D043583:Nucleoside-Triphosphatase / Q000235:genetics / Q000378:metabolism*; D030101:Orthoreovirus, Avian / Q000201:enzymology* / Q000235:genetics; D012313:RNA / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D003067:Coenzymes; D008670:Metals; D011994:Recombinant Proteins; D014764:Viral Proteins; D012313:RNA; D017766:Acid Anhydride Hydrolases; C023090:RNA triphosphatase; D043583:Nucleoside-Triphosphatase