Human DNA ligase 1 (LIG1) performs the final step in DNA repair and recombination pathways by sealing DNA breaks, and it functions as the main replicative ligase. Hypomorphic LIG1 variants R771W and R641L cause immune deficiencies in LIG1 Syndrome patients. In vitro these LIG1 variants have decreased catalytic efficiency and increased abortive ligation and it is not known if either biochemical defect is sufficient on its own to cause immune deficiency. We investigated the enzymatic activity of several new candidate LIG1 Syndrome variants chosen based on their structural proximity to known clinical variants, low minor allele frequency (MAF), high level of conservation, and concurrence in patients with similar symptoms as LIG1 Syndrome patients. The R305Q substitution is in the DNA binding domain, R768W is in the OB-fold domain, and R641S is in the nucleotidyltransferase domain. Biochemical characterization confirmed deficiencies in ligase activity for all three variants, but also revealed marked differences in comparison to the known LIG1 Syndrome variants. Both the R305Q and R768W substitutions increase the KM for DNA and decrease the catalytic efficiency, however, neither exhibit elevated levels of abortive ligation. In contrast, the R641S variant exhibits a greater impairment of activity as well as a more pronounced level of abortive ligation compared to the known LIG1 Syndrome variant, R641L. This work expands the number of LIG1 alleles that are likely candidates for LIG1 Syndrome, and it raises the question of whether distinct enzymatic deficiencies in LIG1 cause unique clinical impacts in patients harboring these alleles.

中文翻译：

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DNA 连接酶 1 的罕见变体显示出不同的缺陷机制


人 DNA 连接酶 1 （LIG1） 通过密封 DNA 断裂来执行 DNA 修复和重组途径的最后一步，它作为主要的复制连接酶发挥作用。亚型LIG1变异R771W和R641L会导致LIG1综合征患者的免疫缺陷。在 体外，这些 LIG1 变体的催化效率降低并增加了流产连接，目前尚不清楚任何一种生化缺陷本身是否足以导致免疫缺陷。我们研究了几种新的候选 LIG1 综合征变体的酶活性，这些变体是根据它们在结构上与已知临床变体的结构接近性、低次要等位基因频率 （MAF）、高水平的保守性以及与 LIG1 综合征患者具有相似症状的患者的一致性而选择的。R305Q 取代位于 DNA 结合结构域，R768W 位于 OB 折叠结构域，R641S 位于核苷酸转移酶结构域。生化表征证实了所有三种变体的连接酶活性缺陷，但也揭示了与已知的 LIG1 综合征变体相比的显着差异。R305Q 和 R768W 取代均增加 DNA 的 KM 并降低催化效率，然而，两者都没有表现出异常连接水平升高。相比之下，与已知的 LIG1 综合征变体 R641L 相比，R641S 变体表现出更大的活性损害以及更明显的流产连接水平。这项工作扩大了可能成为 LIG1 综合征候选者的 LIG1 等位基因的数量，并提出了一个问题，即 LIG1 中不同的酶缺陷是否会对携带这些等位基因的患者造成独特的临床影响。