{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nMammalian polynucleotide kinase/phosphatase (PNKP) is an essential dual‐function enzyme that plays a central role in DNA repair by processing the damaged termini of DNA breaks. Its two catalytic activities—5′‐kinase and 3′‐phosphatase—modify DNA ends by phosphorylating 5′‐hydroxyl groups and dephosphorylating 3′‐phosphate termini, respectively, preparing them for subsequent ligation. Structural studies reveal that the enzyme possesses a broad substrate pocket in its kinase domain, favoring double‐stranded substrates with recessed 5′ ends, while its phosphatase domain readily engages single-stranded or frayed 3′-phosphorylated termini. These studies illustrate the molecular determinants of substrate recognition and the flexibility afforded by the tethered FHA domain that recruits PNKP to repair complexes through interactions with phosphorylated proteins."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn vivo, proper PNKP function is critical for maintaining genomic stability, especially in neural tissues. Attenuation or loss of PNKP activity has been linked to aberrant neurogenesis, manifesting as severe neurodevelopmental defects including microcephaly and early postnatal lethality. Furthermore, compromised PNKP-mediated processing of DNA single- and double-strand breaks underlies increased sensitivity to genotoxic stresses—such as DNA-protein crosslinks and oxidative damage—and defective DNA repair associated with the aging phenotypes observed in animal models. The recruitment of PNKP via interactions with scaffold proteins such as XRCC1 underscores the coordinated assembly of repair complexes in response to DNA damage."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "6"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nMoreover, emerging evidence indicates that PNKP function is further modulated by interactions with other nuclear factors. Notably, its association with PFKFB3, and the consequent dependency on fructose-2,6-bisphosphate, highlights a link between DNA repair regulation and cellular metabolism. Restoration of this cofactor has been shown to rescue PNKP activity and genome integrity in neurodegenerative conditions such as Huntington’s disease and spinocerebellar ataxia type 3, suggesting therapeutic potential through metabolic modulation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Nina K Bernstein, R Scott Williams, Melissa L Rakovszky, et al. 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"}, {"type": "b", "children": [{"type": "t", "text": "Polynucleotide kinase-phosphatase enables neurogenesis via multiple DNA repair pathways to maintain genome stability."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "EMBO J (2015)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.15252/embj.201591363"}], "href": "https://doi.org/10.15252/embj.201591363"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "26290337"}], "href": "https://pubmed.ncbi.nlm.nih.gov/26290337"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Julie K Horton, Donna F Stefanick, Ming-Lang Zhao, et al. "}, {"type": "b", "children": [{"type": "t", "text": "XRCC1-mediated repair of strand breaks independent of PNKP binding."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "DNA Repair (Amst) (2017)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.dnarep.2017.10.007"}], "href": "https://doi.org/10.1016/j.dnarep.2017.10.007"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "29100039"}], "href": "https://pubmed.ncbi.nlm.nih.gov/29100039"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Wisoo Shin, Whitney Alpaugh, Laura J Hallihan, et al. "}, {"type": "b", "children": [{"type": "t", "text": "PNKP is required for maintaining the integrity of progenitor cell populations in adult mice."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Life Sci Alliance (2021)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.26508/lsa.202000790"}], "href": "https://doi.org/10.26508/lsa.202000790"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "34226276"}], "href": "https://pubmed.ncbi.nlm.nih.gov/34226276"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Anirban Chakraborty, Sravan Gopalkrishnashetty Sreenivasmurthy, Wyatt Miller, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Fructose-2,6-bisphosphate restores DNA repair activity of PNKP and ameliorates neurodegenerative symptoms in Huntington's disease."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Proc Natl Acad Sci U S A (2024)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1073/pnas.2406308121"}], "href": "https://doi.org/10.1073/pnas.2406308121"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "39298485"}], "href": "https://pubmed.ncbi.nlm.nih.gov/39298485"}]}]}]}