Probing the Conformational Changes Associated with DNA Binding to PARP1

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Poly(ADP-ribose) polymerase 1 (PARP1) is vital for DNA repair and a target for cancer therapy.
• PARP inhibitors (PARPi) are approved for BRCA-negative cancers, but their trapping mechanisms remain unclear.
• Understanding PARP1 trapping is key to optimizing PARPi efficacy and reducing toxicity.

Purpose of the Study:

• Investigate the binding properties of PARP1 to DNA with double-strand breaks.
• Clarify the relationship between PARP1 DNA binding, conformational changes, and inhibitor interactions.
• Determine if PARPi affect the allosteric coupling between DNA binding and catalytic activation.

Main Methods:

• Utilized sequential mixing stopped-flow spectroscopy to study PARP1-DNA interactions.
• Employed varying DNA concentrations and PARP1 mutants to analyze binding kinetics.
• Monitored conformational changes associated with DNA binding and activation.

Main Results:

• Identified a slow conformational change in PARP1 following rapid DNA binding.
• Demonstrated this conformational change is part of the 'monkey bar mechanism' for DNA-dependent dissociation.
• Linked this conformational change to DNA-dependent PARP1 activation.
• Found no evidence that PARPi perturb the allosteric coupling between DNA binding and activation.

Conclusions:

• PARP1's DNA binding and activation involve a specific conformational change.
• PARP inhibitors do not appear to disrupt the allosteric pathway linking DNA binding to activation.
• Further research is needed to fully elucidate PARPi trapping mechanisms and their impact on DNA repair.