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

ABSTRACT: PARP1 and PARP2 recognize DNA breaks immediately upon their formation, generate a burst of local PARylation to signal their location, and are co-targeted by all current FDA-approved forms of PARP inhibitors (PARPi) used in the cancer clinic. Recent evidence indicates that the same PARPi molecules impact PARP2 differently from PARP1, raising the possibility that allosteric activation may also differ. We find that unlike for PARP1, destabilization of the autoinhibitory domain of PARP2 is insufficient for DNA damage-induced catalytic activation. Rather, PARP2 activation requires further unfolding of an active site α-helix. In contrast, the corresponding α-helix in PARP1 only transiently forms, even prior to engaging DNA. Only one clinical PARPi, Olaparib, stabilizes the PARP2 active site α-helix, representing a structural feature with the potential to discriminate small molecule inhibitors. Collectively, our findings reveal unanticipated differences in local structure and changes in activation-coupled backbone dynamics between PARP1 and PARP2.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Emily Smith

LAB HEAD: Dr. Ben

PROVIDER: PXD043794 | Pride | 2024-09-30

REPOSITORIES: Pride

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Project description:Poly(ADP-ribose) polymerase 1 (PARP1) is a highly conserved nuclear protein in multicellular organisms that modulates chromatin opening, and by doing so, it plays a significant role in gene expression regulation during development and differentiation. Despite its significance, all reported Parp1 total knockout mice strains are viable and fertile with no developmental anomalies. It was previously believed that functional redundancy with other PARP family members explain such a controversy. PARP2 is the main candidate to fulfill PARP1 functions in Parp1 knockout mice. Indeed, Parp1 Parp2 double knockout mice are arrested early in development and unable to proceed through gastrulation. However, while PARP2 has similar catalytic domain to PARP1, it lacks other domains that play important regulatory roles, thus making the lack of developmental problems in Parp1 mice total knockouts highly unlikely. To address this question, we checked the best investigated and publicly available Parp1 knockout mice strain. We found that Parp1 is still expressed in these mice, based on the presence of its mRNA transcript. Contrary to prior assumptions, we identified persistent mRNA expression in knockout mice, albeit at reduced levels. Detailed transcript analysis revealed an alternatively spliced PARP1 variant lacking exon two with introduced artificial cassette. Subsequent protein analysis confirmed the existence of a truncated PARP1 protein in knockout mice. We established embryonic stem cell lines from knockout mice and revealed the presence of pADPr. The decreased level of pADPr was detected in knockout ES cells with Western Blotting analysis, but immunofluorescence staining didn’t detect any difference in distribution or level of pADPr in nuclei of knockout ES cells compared to control ones. Moreover, in double Parp1 Parg mutant ES cells the accumulation of pADPr greatly exceeded its amount in normal and even in hypomorph Parg mutant ES cells, suggesting the presence of functionally active PARP1. Therefore, our findings challenge the conventional understanding of PARP1 depletion effects.

			Action	DRS
	20210806_FD_PARP2.raw	Raw
	20210902_ND_PARP2_1.raw	Raw
	20210902_PARP2_1.raw	Raw
	20210902_PARP2_2.raw	Raw
	20210902_PARP2_dgap_1.raw	Raw

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

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