Alkylated DNA base damage, one of the most common cytotoxic and mutagenic DNA lesions, is classically repaired by lesion-specific DNA glycosylases, which excise alkylated bases to create abasic sites and initiate the base-excision repair (BER) pathway. DNA alkylation repair is critical for genome stability and furthermore a major resistance factor for cancer chemotherapies, so the other less studied but biologically key alkylation repair pathways merit characterization. This proposal thus focuses upon important non-glycosylase pathways, whereby alkylation damage is removed by direct reversal (Aim 1), or by pathway `crosstalk'proteins that non-classically guide damage into one of the major DNA-excision repair pathways (Aims 2-4) to avoid release of toxic DNA species. Our efforts to date have helped elucidate the structural chemistry for human direct reversal proteins AGT (O6- alkylguanine-DNA-alkyltransferases) and ABH3 (the dealkylation dioxygenase AlkB homolog 3) and support their further characterizations proposed in Aim 1. We moreover discovered three systems to characterize crosstalk, an important cellular strategy for alkylation repair pathway intersection that promotes the non-classical entry of damaged DNA into excision repair pathways. We will therefore furthermore characterize three specific alkylation base damage response proteins that promote non- classical entry into each of the three prototypic pathways for DNA excision repair:
Aim 2) ATL (alkyl- transferase-like) that is transferase-inactive but genetically connected to nucleotide excision repair (NER), which excises bulky lesions that distort DNA, Aim 3) AGTendoV (O6-alkylguanine-DNA- alkyltransferase-endonucleaseV) that covalently connects AGT with the Endo V DNA backbone excision enzyme to form breaks that are substrates for BER, and Aim 4) glycosylase-inactive Mag2 (methyl-adenine-glycosylase homolog 2) that genetically and structurally connects to mismatch repair (MMR) that classically excises mismatched regions. We propose to integrate quantitative biophysical characterization of proteins and complexes by macromolecular X-ray crystallography (MX) and small angle X-ray scattering in solution (SAXS) in the Tainer lab with complementary detailed in vitro and in vivo biochemical and mutational results from the Pegg lab. The proposed work will characterize core alkylation repair initiation proteins and their in vivo functions to elucidate structure-function mechanisms for key facets of non-glycosylase alkylation damage repair. Overall, these results will provide a unified understanding of alkylation damage responses relevant to genetic integrity, to chemotherapy resistance, and to promoting advances in alkylation inhibitors for cancer therapies. Results obtained will therefore shed light on DNA alkylation repair proteins, their inhibitors, and steps relevant to novel therapeutic strategies and cancer chemotherapies. DNA alkylation is a source of genomic instability leading to cancer predispositions, and is also a major result of cancer chemotherapies. Alkylation damage can be removed directly by reversing the base damage or by the recruitment of non-classical repair machinery to correct the lesion;yet, neither the structural chemistries nor the mechanisms of `crosstalk'mediated by these pathways are fully understood. We propose to characterize the structural cell biology of these two key facets of alkylation damage repair, which are directly relevant to improved cancer chemotherapies and risk assessments for environmental agents.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Knowlton, John R
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Scripps Research Institute
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Fang, Qingming (2013) DNA-protein crosslinks processed by nucleotide excision repair and homologous recombination with base and strand preference in E. coli model system. Mutat Res 741-742:1-10
Tsai, Chi-Lin; Tainer, John A (2013) Probing DNA by 2-OG-dependent dioxygenase. Cell 155:1448-50
Dalhus, Bjørn; Nilsen, Line; Korvald, Hanne et al. (2013) Sculpting of DNA at abasic sites by DNA glycosylase homolog mag2. Structure 21:154-166
Wilkinson, Oliver J; Latypov, Vitaly; Tubbs, Julie L et al. (2012) Alkyltransferase-like protein (Atl1) distinguishes alkylated guanines for DNA repair using cation-? interactions. Proc Natl Acad Sci U S A 109:18755-60
Latypov, Vitaly F; Tubbs, Julie L; Watson, Amanda J et al. (2012) Atl1 regulates choice between global genome and transcription-coupled repair of O(6)-alkylguanines. Mol Cell 47:50-60
Tubbs, Julie L; Tainer, John A (2011) P53 conformational switching for selectivity may reveal a general solution for specific DNA binding. EMBO J 30:2099-100
Pegg, Anthony E (2011) Multifaceted roles of alkyltransferase and related proteins in DNA repair, DNA damage, resistance to chemotherapy, and research tools. Chem Res Toxicol 24:618-39
Tubbs, Julie L; Tainer, John A (2010) Alkyltransferase-like proteins: molecular switches between DNA repair pathways. Cell Mol Life Sci 67:3749-62
Fang, Qingming; Kanugula, Sreenivas; Tubbs, Julie L et al. (2010) Repair of O4-alkylthymine by O6-alkylguanine-DNA alkyltransferases. J Biol Chem 285:8185-95
Aramini, James M; Tubbs, Julie L; Kanugula, Sreenivas et al. (2010) Structural basis of O6-alkylguanine recognition by a bacterial alkyltransferase-like DNA repair protein. J Biol Chem 285:13736-41

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