Ying Li

Publications (4)12.8 Total impact

• Article: Effects of hydrogen peroxide upon nicotinamide nucleotide metabolism in Escherichia coli: changes in enzyme levels and nicotinamide nucleotide pools and studies of the oxidation of NAD(P)H by Fe(III).

  Julia L Brumaghim, Ying Li, Ernst Henle, Stuart Linn
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  ABSTRACT: DNA is damaged in vivo by the Fenton reaction mediated by Fe2+ and cellular reductants such as NADH, which reduce Fe3+ to Fe2+ and allow the recycling of iron. To study the response of Escherichia coli to such cycling, the activities of several enzymes involved in nicotinamide nucleotide metabolism were measured following an H2O2 challenge. NADPH-dependent peroxidase, NADH/NADP+ transhydrogenase, and glucose-6-phosphate dehydrogenase were most strongly induced, increasing 2.5-3-fold. In addition, the cellular ratios of NADPH to NADH increased 6- or 92-fold 15 min after exposure to 0.5 or 5 mm H2O2, respectively. In vitro, NADH was oxidized by Fe3+ up to 16-fold faster than NADPH, despite their identical reduction potentials. To understand this rate difference, the interactions of Fe3+ and Ga3+ with NAD(P)H were examined by 1H, 13C, and 31P NMR spectroscopy. Association with NADH occurred primarily with adenine at N7 and the amino group, but for NADPH, strong metal interactions also occurred at the 2'-phosphate group. Interaction of M3+ (Fe3+ or Ga3+) with the adenine ring would bring it into close proximity to the redox-active nicotinamide ring in the folded form of NAD(P)H, but interaction of M3+ with the 2'-phosphate group would avoid this close contact. In addition, as determined by absorbance spectroscopy, the energy of the charge-transfer species was significantly higher for the Fe3+.NADPH complex than for the Fe3+.NADH complex. We therefore suggest that upon exposure to H2O2 the NADH pool is depleted, and NADPH, which is less reactive with Fe3+, functions as the major nicotinamide nucleotide reductant.
  Journal of Biological Chemistry 11/2003; 278(43):42495-504. · 4.77 Impact Factor
• Source

  Available from: ncbi.nlm.nih.gov

  Article: Stimulation of human DNA polymerase epsilon by MDM2.

  Hitomi Asahara, Ying Li, Jill Fuss, Dale S Haines, Nikolina Vlatkovic, Mark T Boyd, Stuart Linn
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  ABSTRACT: The human DNA polymerase epsilon catalytic subunit consists of a 140-kDa N-terminal domain that contains the catalytic activity and a 120-kDa C-terminal domain that binds to the other subunits and to exogenous peptides, including PCNA and MDM2. We report here that recombinant human MDM2 purified from insect cells or Escherichia coli stimulated the activity of DNA polymerase epsilon up to 10- and 40-fold, respectively, but not those of DNA polymerase beta or Klenow fragment of E.coli DNA polymerase I. Kinetic studies indicated that MDM2 increased the maximum velocity of the reaction, but did not change substrate affinities. The stimulation depended upon the interaction of the N-terminal 166 amino acid residues of MDM2 with the C-terminal domain of the full-length catalytic subunit, since the deletion of 166 amino acids from N-terminal of MDM2 or the removal of the C-terminal domain of DNA polymerase epsilon by trypsin digestion or competition for binding to it by the addition of excess C-terminal fragment eliminated the stimulation. Since DNA polymerase epsilon appears to be involved in DNA replication, recombination and repair synthesis, we suggest that MDM2 binding to DNA polymerase epsilon might be part of a reconfiguration process that allows DNA polymerase epsilon to associate with repair/recombination proteins in response to DNA damage.
  Nucleic Acids Research 06/2003; 31(9):2451-9. · 8.03 Impact Factor
• Article: MDM2 interacts with the C-terminus of the catalytic subunit of DNA polymerase {varepsilon}

  Nikolina Vlatkovic, Stephanie Guerrera, Ying Li, Stuart Linn, Dale S. Haines, Mark T Boyd
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  ABSTRACT: MDM2 is induced by p53 in response to cellular insults such as DNA damage and can have effects upon the cell cycle that are independent or downstream of p53. We used a yeast two-hybrid screen to identify proteins that bind to MDM2 and which therefore might be involved in these effects. We found that MDM2 can bind to the C-terminus of the catalytic subunit of DNA polymerase ϵ (DNA pol ϵ), to a region that is known to be essential in yeast. In an in vitro system we confirmed that MDM2 could bind to the homologous regions of both mouse and human DNA pol ϵ and to full-length human DNA pol ϵ. DNA pol ϵ co-immunoprecipitated with MDM2 from transfected H1299 cells and also from a HeLa cell nuclear extract. We show here that the DNA pol ϵ-interacting domain of MDM2 is located between amino acids 50 and 166. Our studies provide evidence that MDM2 interacts with a region of DNA pol ϵ that plays a critical role in the function of DNA pol ϵ.
• Article: Stimulation of human DNA polymerase e by MDM2

  Hitomi Asahara, Ying Li, Jill Fuss, Dale S. Haines, Nikolina Vlatkovic, Mark T. Boyd, Stuart Linn
  [show abstract] [hide abstract]
  ABSTRACT: The human DNA polymerase e catalytic subunit consists of a 140-kDa N-terminal domain that con- tains the catalytic activity and a 120-kDa C-terminal domain that binds to the other subunits and to exo- genous peptides, including PCNA and MDM2. We report here that recombinant human MDM2 purified from insect cells or Escherichia coli stimulated the activity of DNA polymerase e up to 10- and 40-fold, respectively, but not those of DNA polymerase b or Klenow fragment of E.coli DNA polymerase I. Kinetic studies indicated that MDM2 increased the maximum velocity of the reaction, but did not change substrate affinities. The stimulation depended upon the interaction of the N-terminal 166 amino acid residues of MDM2 with the C-terminal domain of the full-length catalytic subunit, since the deletion of 166 amino acids from N-terminal of MDM2 or the removal of the C-terminal domain of DNA polymerase e by trypsin digestion or com- petition for binding to it by the addition of excess C-terminal fragment eliminated the stimulation. Since DNA polymerase e appears to be involved in DNA replication, recombination and repair synthe- sis, we suggest that MDM2 binding to DNA polymer- ase e might be part of a reconfiguration process that allows DNA polymerase e to associate with repair/recombination proteins in response to DNA damage.