Date of Award
Doctor of Philosophy (PhD)
Biochemistry and Molecular Biology
Chen , Chin-Fu
Ingram-Smith , Cheryl
Luo , Feng
Living organisms are exposed a nitrosative stress mediated by reactive nitrogen species (RNS) that can cause DNA damage and mutation. DNA base deamination is a typical damage occurred under nitrosative stress, which results in conversion of cytosine (C) to uracil (U), adenine (A) to hypoxanthine (I), and guanine (G) to xanthine (X) or oxanine (O). Base excision repair (BER) is an important pathway to remove deaminated DNA lesions in mammalian and microbial systems. My dissertation work concerns with genes and enzymes involved in resistance to nitrosative stress and DNA glycosylases in the BER pathway. In chapter one, I will briefly review current knowledge in these areas. In chapter two, I will present a genetic and biochemical investigation that identifies mouse thioredoxin domain-containing 5 (mTrx 5) and Escherichia coli thioredoxin 1 and thioredoxin 2 as genes that are involved in resistance to nitrosative stress. This work indicates radical scavenging as an important resistance mechanism. In chapter three, I will present an extensive biochemical, molecular modeling and molecular dynamics simulations study on deaminated repair activities in E. coli mismatch-specific uracil DNA glycoyslase (MUG). Data obtained from cell extracts and purified enzymes indicate that E. coli MUG is a robust xanthine DNA glycosylase (XDG) although it is well known as a uracil DNA glycosylase. Site-directed mutagenesis, coupled with molecular modeling and molecular dynamics simulations reveal distinct hydrogen bonding patterns in the active site of E. coli MUG, which account for the specificity differences between E. coli MUG and human thymine DNA glycosylase, as well as that between the wild type MUG and mutant MUG enzymes. In chapter four, I will describe the deaminated base repair of DNA glycosylases in archaea. Overall, these studies provide new insights on the cellular mechanisms in resistance to nitrosative stress and deaminated DNA repair mechanisms in mammalian and microbial systems.
Lee, Hyun-wook, "RESISTANCE AND DNA REPAIR MECHANISMS UNDER NITROSATIVE STRESS IN MAMMALIAN AND MICROBIAL SYSTEMS" (2010). All Dissertations. 657.