The BRCT Domain of PARP1 Binds Intact DNA and Mediates Intrastrand Transfer

Abstract

Poly(ADP-ribose) polymerase 1 (PARP1) is a key player in the response to DNA damage and is the target of four different clinical inhibitors used for the treatment of cancers. Binding of PARP1 to damaged DNA leads to activation via destabilization of a subdomain of the catalytic domain, and activated PARP1 utilizes NAD+ to add chains of poly(ADP-ribose) onto itself and other nuclear proteins. PARP1 also binds abundantly to intact DNA and chromatin, where it remains enzymatically inactive. Here we show that intact DNA makes contacts with the BRCT domain, which was not previously recognized as a DNA-binding domain. This binding mode does not result in the concomitant reorganization and activation of the catalytic domain. We visualize the BRCT domain bound to nucleosomal DNA by cryogenic electron microscopy (cryoEM) and identify a key motif conserved from ancestral BRCT domains for binding phosphates on DNA and phospho-peptides. Finally, we demonstrate that the DNA-binding properties of the BRCT domain contribute to the ‘monkey-bar mechanism’ that mediates transfer of PARP1 from one DNA segment to another.