Recognition of G-Quadruplexes by the FANCJ AKKQ Peptide

G-quadruplexes (G4s) are stable structures formed by Hoogsteen hydrogen bonding between four stretches of three or more consecutive guanines. If left accumulated, G4s can disrupt DNA replication, repair, and RNA transcription. Additionally, guanines are susceptible to damage from reactive oxygen species that cause guanine to thymine transversion mutations. FANCJ is a DNA helicase that participates in the repair of interstrand DNA crosslinks in human cells. FANCJ has been shown to support DNA replication through guanine rich sequences by unfolding G4 structures. Previous research has shown that FANCJ possesses an “AKKQ” amino acid motif that target G4s and is thought to target 8-oxoguanine modified G4 sequences (8oxoG4s). We hypothesize that the molecular recognition of FANCJ to 8oxoG4s is correlated to the DNA damage position, sequence composition, and stability of the substrate. To test this, we have measured the binding affinity of the FANCJ AKKQ peptide to G4 DNA that can adopt parallel, antiparallel, or hybrid spatial configurations, and we have systematically replaced the guanine bases with 8oxoGs. Circular dichroism spectroscopy (CD) was used to define the conformation of the G4 DNA, and CD data were collected as a function of solution conditions to determine the melting temperature. Fluorescence spectroscopy was used to measure the binding affinities of FANCJ AKKQ to the library of G4 DNA. These experimental outcomes will provide a detailed view of how 8oxoGs affect the physical properties of G4s and their molecular recognition by FANCJ.