Research

Human genetic material DNA is susceptible to various endogenous and foreign chemicals, producing as many as 100,000 chemically modified DNA lesions or DNA adducts per cell each day. DNA damage is guarded by an intricate DNA repair network; however, certain DNA lesions can escape repair or exceed the repair capacity and eventually accumulate in the genome. The persisted DNA lesions can interfere with DNA metabolisms, lead to replication errors, replication fork collapse, or cell death. An altered genetic content in key regions, such as proto-oncogenes and tumor suppressor genes, is a major driving force for human diseases including cancer.

One aspect of our research focuses on understanding the molecular mechanisms by which translesion synthesis (TLS) DNA polymerases catalyze nucleotide incorporation, interact with cognate proteins, and form faulty products. TLS is a conversed DNA damage tolerance mechanism, whereby specialized DNA polymerases participate in copying past obstructive DNA structures, such as DNA lesions or non-canonical DNA structures. Because TLS is error-prone, it plays an important role in mutagenesis.

We combine classic enzymology and biophysical approaches (e.g. enzyme kinetics and X-ray crystallography) with modern mass spectrometry-based methods to gain mechanistic insights into TLS DNA polymerases. For example, we uncovered the mechanism of DNA replication-blocking for the (5’S)-8,5’-cyclo-2’-deoxyguanosine DNA lesion by demonstrating an unusual 5’-template base clustering at the active site of DNA polymerase in our X-ray crystal structures (Biochemistry, 2015, 54, 639-651). This lesion is formed during ionizing radiation or endogenous oxidative metabolisms, and has been implicated in Xeroderma pigmentosum, Cockayne syndrome, and breast cancer.

In addition, we demonstrated the importance of human DNA polymerase η in error-prone replication past an oxidized abasic lesion-induced DNA interstrand cross-link (ICL) (Biochemistry, 54, 7409-7422). ICLs are considered to be extremely cytotoxic lesions that block a variety of DNA metabolisms. Many cancer chemotherapies work by forming ICLs in cancer cells. Recently, we illuminated the basis of the low carcinogenic risk of lucidin (a natural product and DNA-damaging reagent) in humans by providing biochemical and structural evidence for the error-free bypass of human DNA polymerase κ (Chem. Res. Toxicol. 2017, 30, 2023-2032). Collectively, these studies have provided kinetic, molecular, and structural basis for translesion synthesis and advanced the mechanistic understanding of their contributions to genomic instability.

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