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

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Poly(ADP-ribose) polymerase 1 (PARP1) and PARP2 are crucial in DNA damage response.
• PARP inhibitors (PARPi) are FDA-approved cancer therapeutics targeting both enzymes.
• Emerging data suggests differential effects of PARPi on PARP1 versus PARP2.

Purpose of the Study:

• To investigate the distinct mechanisms of catalytic activation between human PARP1 and PARP2.
• To explore structural differences in enzyme activation and their implications for PARP inhibitor selectivity.

Main Methods:

• Comparative analysis of PARP1 and PARP2 activation pathways.
• Structural and dynamic studies of enzyme activation upon DNA damage.
• Assessment of PARP inhibitor interactions with PARP2 active site structures.

Main Results:

• PARP2 activation requires unfolding of an active site helix, unlike PARP1.
• PARP1's active site helix is transiently formed even before DNA binding.
• Olaparib is the only clinical PARPi that stabilizes the PARP2 active site helix.

Conclusions:

• Human PARP1 and PARP2 exhibit distinct structural dynamics during activation.
• The PARP2 active site helix stabilization by Olaparib presents a potential basis for inhibitor selectivity.
• These findings reveal novel differences in enzyme activation relevant to cancer therapy.