Structural and functional studies of DNA mismatch repair proteins

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The integrity of DNA is constantly threatened by damaging insults that can lead to chromosomal rearrangements or cell death. The long-term goal of our research program is to understand how DNA damage is efficiently repaired, in turn preventing genome instability. One of the most fascinating aspects of the DNA damage response is how repair proteins find the lesions regardless of context, thereby ensuring the repair of each and every lesion. Our laboratory studies how the proteins that cut DNA based on its shape (known as structure-specific nucleases) recognize and cut their target DNA. Our overarching hypothesis is that structure-specific nucleases use common DNA binding mechanisms, but achieve specificity through their interaction with pathway-specific factors. To probe this idea, we will use a combination of biochemical, biophysical and structural biology techniques to study how structure-specific nucleases in two DNA repair pathways bind and cut DNA. DNA mismatch repair corrects errors that occur while DNA is being copied. Two conserved proteins are essential for this process: MutS and MutL. Over the years, my laboratory has made key contributions to the functions of MutL. However, MutL does not look like any other nuclease and, therefore, we do not understand how it cuts DNA yet. In the next five years, we will address this question by determining the 3-dimensional structure of MutL bound to DNA. Leveraging our experience with MutL, we have recently broaden the scope of our research program to characterize structure-specific nucleases in other repair pathways. Breaks affecting both DNA strands are the most dangerous form of damage because the broken pieces do not retain information of their context. Single strand-annealing repairs double-strand breaks between adjacent repeat sequences. Although this repair mechanism causes the loss of genetic information, it is prevalent in humans, due to the high frequency of homologous repeat sequences present in our genome. We will determine how the adaptor protein Saw1 recruits the structure-specific nuclease Rad1-Rad10 to repair intermediates. This is important because Rad1-Rad10 can process several types of damage and, therefore, the adaptor proteins determine the lesion to be processed. Our work will provide fundamental mechanistic insights into the roles of these two nucleases in DNA repair and genome maintenance. The latter is specially important for healthy aging. Canada has been described as a “greying nation” because it has more people over 65 than under 15, underscoring the indirect benefits of our research.