Connecting the Dots: APE1’s Association to ALS

• Oviyanna Umoh, Neuroscience, University of Delaware

• Amy Whitaker, Nuclear Dynamics and Cancer, Fox Chase Cancer Center

Amyotrophic Lateral Sclerosis (ALS), the most prevalent motor neuron disease, is characterized by its progressive degeneration of motor neurons, leading to muscle weakness, paralysis, and eventual respiratory failure. Our understanding of ALS’ pathogenesis is underdeveloped and enigmatic given that most cases are sporadic. However, functional defects in our DNA repair genes likely contribute to the disease’s development. DNA damage induced by oxidative stress forms lesions known as apurinic/apyrimidinic (AP) sites. To counteract this cellular damage, the enzyme apurinic/apyrimidinic endonuclease 1 (APE1) initiates AP site repair through the base excision repair pathway (BER). Damage or variations in APE1 have been associated with increased susceptibilities to numerous diseases. Several APE1 variations have been identified in individuals with ALS including E126D, D283G, and G306A. We hypothesized that these APE1 variants impact the structure and function of APE1, playing an important role in the development of ALS. X-ray crystallography, which determines the three-dimensional structure of proteins, revealed significant structural differences within the active site of the APE1 variants. Additionally, fluorescence polarization revealed reduced binding affinity between the APE1 variants and DNA. Enzyme kinetics studies, which measure the rate at which enzymes convert substrate into product, revealed slower catalytic activity of the APE1 variants in comparison to wild-type. These results suggest that E126D, D283G, and G306A mutations in APE1 cause structural and functional changes, potentially contributing to ALS’ development by impairing DNA repair. Future work could explore protein-to-protein interaction differences between the variations and other BER enzymes. Ultimately, this data enhances our understanding of the molecular mechanisms causing ALS and may contribute to the development of diagnostic tools for the disease.