Search results for: hoGG1 Enzyme & Buffer
#27571472 
2016/09/07
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Comparative Effects of Ions, Molecular Crowding, and Bulk DNA on the Damage Search Mechanisms of hOGG1 and hUNG.
The energetic nature of the interactions of DNA base excision repair glycosylases with undamaged and damaged DNA and the nuclear environment are expected to significantly impact the time it takes for these enzymes to search for damaged DNA bases. In particular, the high concentration of monovalent ions, macromolecule crowding, and densely packed DNA chains in the cell nucleus could alter the search mechanisms of these enzymes as compared to findings in dilute buffers typically used in in vitro experiments. Here we utilize an in vitro system where the concerted effects of monovalent ions, macromolecular crowding, and high concentrations of bulk DNA chains on the activity of two paradigm human DNA glycosylases can be determined. We find that the energetic nature of the observed binding free energies of human 8-oxoguanine DNA glycosylase (hOGG1) and human uracil DNA glycosylase (hUNG) for undamaged DNA are derived from different sources. Although hOGG1 uses primarily nonelectrostatic binding interactions with nonspecific DNA, hUNG uses a salt-dependent electrostatic binding mode. Both enzymes turn to a nonelectrostatic mode in their specific complexes with damaged bases in DNA, which enhances damage site specificity at physiological ion concentrations. Neither enzyme was capable of efficiently locating and removing their respective damaged bases in the combined presence of physiological ions and a bulk DNA chain density approximating that found in the nucleus. However, the addition of an inert crowding agent to mimic macromolecular crowding in the nucleus largely restored their ability to track DNA chains and locate damaged sites. These findings suggest how the concerted action of monovalent ions and crowding could contribute to efficient DNA damage recognition in cells.Shannen L Cravens, James T Stivers
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#23607987 2013/04/19
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Expression of human oxoguanine glycosylase 1 or formamidopyrimidine glycosylase in human embryonic kidney 293 cells exacerbates methylmercury toxicity in vitro.
Exposure to methylmercury (MeHg) acutely at high levels, or via chronic low-level dietary exposure from daily fish consumption, can lead to adverse neurological effects in both the adult and developing conceptus. To determine the impact of variable DNA repair capacity, and the role of reactive oxygen species (ROS) and oxidatively damaged DNA in the mechanism of toxicity, transgenic human embryonic kidney (HEK) 293 cells that stably express either human oxoguanine glycosylase 1 (hOgg1) or its bacterial homolog, formamidopyrimidine glycosylase (Fpg), which primarily repair the oxidative lesion 8-oxo-2'-deoxyguanosine (8-oxodG), were used to assess the in vitro effects of MeHg. Western blotting confirmed the expression of hOgg1 or Fpg in both the nuclear and mitochondrial compartments of their respective cell lines. Following acute (1-2h) incubations with 0-10μM MeHg, concentration-dependent decreases in clonogenic survival and cell growth accompanied concentration-dependent increases in lactate dehydrogenase (LDH) release, ROS formation, 8-oxodG levels and apurinic/apyrimidinic (AP) sites, consistent with the onset of cytotoxicity. Paradoxically, hOgg1- and Fpg-expressing HEK 293 cells were more sensitive than wild-type cells stably transfected with the empty vector control to MeHg across all cellular and biochemical parameters, exhibiting reduced clonogenic survival and cell growth, and increased LDH release and DNA damage. Accordingly, upregulation of specific components of the base excision repair (BER) pathway may prove deleterious potentially due to the absence of compensatory enhancement of downstream processes to repair toxic intermediary abasic sites. Thus, interindividual variability in DNA repair activity may constitute an important risk factor for environmentally-initiated, oxidatively damaged DNA and its pathological consequences.Stephanie L Ondovcik, Thomas J Preston, Gordon P McCallum, Peter G Wells