Xeroderma pigmentosum (XP) is a heritable disease whose symptoms include inability to tolerate sunlight and a high risk of developing skin cancer. In severe cases, neurodegenerative effects are seen, with loss of mental and sensory capabilities. XP is caused by mutations in one or more of the seven XP proteins, termed XPA through XPG. XP proteins are critical components of the nucleotide excision repair (NER) pathway, and mutations in these patients’ proteins are known to disrupt DNA repair. Therefore, when a patient is exposed to mutagens such as ultraviolet light, DNA damage cannot be properly repaired because the XP protein complex is not fully functional. Importantly, XPA is often correlated to the most severe symptoms of XP, including neurodegeneration.

XPA functions as a scaffold for the multi-protein NER machinery, helping to assemble the complex and position the critical nucleases XPF-ERCC1 and XPG so that the damage is removed from the DNA strand. XPA performs this function in conjunction with the ubiquitous ssDNA binding protein, replication protein A (RPA), which binds to and protects the undamaged strand and also helps to position other NER proteins including XPA. Many of the disease-causing XPA mutations map to the central DNA binding domain, which overlaps with a binding site for RPA. The goal of my work in the Chazin Laboratory is to first generate XPA mutants and confirm the role of the chosen residues in RPA binding. These are the essential preliminary steps required to determine the importance of XPA binding to RPA for effective NER in cells and establish that this contact is a suitable target for the development of small molecules that inhibit NER. Beyond value to determine the mechanisms of NER, such inhibitors will enable an initial assessment of the potential therapeutic value of suppressing NER as a means to neutralize the upregulation of NER in cancers that are treated with DNA damaging agents such as radiation and cis-platin.

Caeley Gullet is a recipient of the Beckmann Scholarship for 2017-2018.