A PARP2-specific active site α-helix melts to permit DNA damage-induced enzymatic activation

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Therapeutics

Background:

• Poly (ADP-ribose) polymerase 1 (PARP1) and PARP2 are key enzymes in DNA damage response.
• These enzymes are targeted by FDA-approved PARP inhibitors (PARPi) in cancer treatment.
• Emerging data suggest differential effects of PARPi on PARP1 versus PARP2.

Purpose of the Study:

• To investigate the distinct mechanisms of catalytic activation between PARP1 and PARP2.
• To explore structural differences that could explain differential PARPi activity.
• To identify structural features enabling small molecule inhibitor discrimination between PARP1 and PARP2.

Main Methods:

• Comparative biochemical assays to assess enzyme activation.
• Structural analysis focusing on autoinhibitory domains and active site helices.
• Investigation of PARP inhibitor (Olaparib) interactions with PARP1 and PARP2 structures.

Main Results:

• PARP2 activation requires unfolding of an active site α-helix, unlike PARP1.
• Destabilizing the autoinhibitory domain is insufficient for PARP2 activation.
• Olaparib uniquely stabilizes the PARP2 active site α-helix, differentiating it from other PARPi.

Conclusions:

• PARP1 and PARP2 exhibit distinct structural requirements for DNA damage-induced activation.
• The PARP2 active site α-helix is a critical determinant for inhibitor specificity.
• Findings provide a structural basis for understanding differential PARPi efficacy and developing novel inhibitors.