Formation, Degradation, and Bypass of DNA-Protein Crosslinks

Abstract

The preservation of DNA replication is requisite for cellular integrity and prevention of tumor formation and cell death. The Y-family DNA polymerases (Pol eta, kappa, iota, and REV1) are crucial in this process because of their roles in the replication and bypass of DNA lesions and adducts. DNA-peptide crosslinks (DPCs) are formed through the bioactivation of bis-electrophiles such as ethylene dibromide. These electrophiles can bind both peptide and protein targets such as glutathione and alkylguanine DNA-alkyltransferase (AGT) with DNA. Studies has shown that these DPCs are mutagenic as well as cytotoxic to cells. Our hypothesis is that select translesion DNA polymerases are capable of replicating past DNA-peptide cross-links. For this replication to occur, SPRTN (a nuclear protease) will degrade the crosslinked protein to a smaller peptide to allow the DNA polymerase to proceed. Model peptides of varying lengths from the AGT active site, as well as glutathione, were synthesized to determine if the size of the peptide crosslink affects the replication by Y-family DNA polymerases. Results showed that Pol eta was capable of bypassing each of the peptide crosslinks, albeit with low levels of misincorporation and significantly reduced catalytic efficiency. SPRTN was also found to proteolytic degrade AGT crosslinks on DNA, and this degradation does allow replication past the lesion by Pol eta.