Veenstra Jenna H, Chabez Alexandria, Haanen Terrance J, Keranen Austin, Cunningham-Rundles Charlotte, O'Brien Patrick J
Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan, USA.
Department of Medicine, Division of Clinical Immunology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
J Biol Chem. 2024 Dec;300(12):107957. doi: 10.1016/j.jbc.2024.107957. Epub 2024 Nov 5.
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 K 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.
人类DNA连接酶1（LIG1）通过封闭DNA断裂来完成DNA修复和重组途径的最后一步，并且它作为主要的复制连接酶发挥作用。低表达的LIG1变体R771W和R641L会导致LIG1综合征患者出现免疫缺陷。在体外，这些LIG1变体的催化效率降低，流产连接增加，目前尚不清楚这两种生化缺陷单独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与已知临床变体的结构接近性、低次要等位基因频率（MAF）、高保守水平以及与LIG1综合征患者症状相似的患者中的共现情况而选择的。R305Q替代位于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。生化特性证实这三种变体的连接酶活性均有缺陷，但与已知的LIG1综合征变体相比也显示出明显差异。R305Q和R768W替代均增加了对DNA的K值并降低了催化效率，然而，两者均未表现出流产连接水平升高。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。这项工作增加了可能是LIG1综合征候选基因的LIG1等位基因数量，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产生独特的临床影响。
