Department of Pathology, The Gottstein Memorial Cancer Research Center, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2012;7(1):e30189. doi: 10.1371/journal.pone.0030189. Epub 2012 Jan 17.
Loss of Werner syndrome helicase-exonuclease (WRN) or of its homolog Bloom syndrome helicase (BLM) results in different inherited disorders. Whereas Werner syndrome is characterized by premature onset of aging and age-associated diseases, Bloom syndrome involves developmental abnormalities and increased predisposition to diverse malignancies. To identify biochemical differences between WRN and BLM that might contribute to the dissimilar outcomes of their loss, we compared their abilities to unwind and bind in vitro diverse DNA structures. Full-length recombinant WRN and BLM proteins expressed in and purified from Sf9 insect cells unwound to comparable extents and with similar K(m) values partial DNA duplex, splayed arm DNA and G'2 bimolecular quadruplex DNA. However, WRN resolved bubble DNA ∼25-fold more efficiently than BLM. The two enzymes were mainly distinguished by their contrasting abilities to bind DNA. WRN bound partial duplexes, bubble and splayed arm DNA and G'2 bimolecular and G4 four-molecular quadruplexes with dissociation constants of 0.25 to 25 nM. By contrast, BLM formed substantial complexes with only G4 quadruplex DNA while binding only marginally other DNA structures. We raise the possibility that in addition to its enzymatic activities WRN may act as a scaffold for the assembly on DNA of additional DNA processing proteins.
Werner 综合征解旋酶-核酸外切酶（WRN）或其同源物 Bloom 综合征解旋酶（BLM）的缺失会导致不同的遗传性疾病。Werner 综合征的特征是过早衰老和与年龄相关的疾病，而 Bloom 综合征则涉及发育异常和增加多种恶性肿瘤的易感性。为了确定 WRN 和 BLM 之间可能导致其缺失产生不同结果的生化差异，我们比较了它们在体外解开和结合不同 DNA 结构的能力。全长重组 WRN 和 BLM 蛋白在 Sf9 昆虫细胞中表达并纯化，从 Sf9 昆虫细胞中表达并纯化，它们在解开部分 DNA 双链体、分叉臂 DNA 和 G'2 双分子四链体 DNA 方面的程度相当，且具有相似的 K(m) 值。然而，WRN 解开泡状 DNA 的效率比 BLM 高约 25 倍。这两种酶的主要区别在于它们结合 DNA 的能力不同。WRN 结合部分双链体、泡状和分叉臂 DNA 以及 G'2 双分子和 G4 四分子四链体的解离常数为 0.25 至 25 nM。相比之下，BLM 仅与 G4 四链体 DNA 形成大量复合物，而仅与其他 DNA 结构略有结合。我们提出这样一种可能性，即除了其酶活性外，WRN 可能作为组装在 DNA 上的其他 DNA 加工蛋白的支架发挥作用。
