Rajan Rakhi, Osterman Amy, Mondragón Alfonso
Department of Molecular Biosciences, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA.
Department of Molecular Biosciences, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA
Nucleic Acids Res. 2016 Apr 20;44(7):3464-74. doi: 10.1093/nar/gkw122. Epub 2016 Feb 22.
Topoisomerase V (Topo-V) is the only topoisomerase with both topoisomerase and DNA repair activities. The topoisomerase activity is conferred by a small alpha-helical domain, whereas the AP lyase activity is found in a region formed by 12 tandem helix-hairpin-helix ((HhH)2) domains. Although it was known that Topo-V has multiple repair sites, only one had been mapped. Here, we show that Topo-V has three AP lyase sites. The atomic structure and Small Angle X-ray Scattering studies of a 97 kDa fragment spanning the topoisomerase and 10 (HhH)2 domains reveal that the (HhH)2 domains extend away from the topoisomerase domain. A combination of biochemical and structural observations allow the mapping of the second repair site to the junction of the 9th and 10th (HhH)2 domains. The second site is structurally similar to the first one and to the sites found in other AP lyases. The 3rd AP lyase site is located in the 12th (HhH)2 domain. The results show that Topo-V is an unusual protein: it is the only known protein with more than one (HhH)2 domain, the only known topoisomerase with dual activities and is also unique by having three AP lyase repair sites in the same polypeptide.
拓扑异构酶V（Topo-V）是唯一兼具拓扑异构酶活性和DNA修复活性的拓扑异构酶。其拓扑异构酶活性由一个小的α-螺旋结构域赋予，而AP裂解酶活性则存在于由12个串联的螺旋-发夹-螺旋（(HhH)2）结构域形成的区域。尽管已知Topo-V有多个修复位点，但仅定位了一个。在此，我们表明Topo-V有三个AP裂解酶位点。对一个跨越拓扑异构酶结构域和10个(HhH)2结构域的97 kDa片段进行的原子结构和小角X射线散射研究表明，(HhH)2结构域从拓扑异构酶结构域向外延伸。生化观察和结构观察相结合，将第二个修复位点定位到第9个和第10个(HhH)2结构域的交界处。第二个位点在结构上与第一个位点以及其他AP裂解酶中的位点相似。第三个AP裂解酶位点位于第12个(HhH)2结构域。结果表明Topo-V是一种独特的蛋白质：它是唯一已知的具有多个(HhH)2结构域的蛋白质，唯一已知的具有双重活性的拓扑异构酶，并且在同一多肽中具有三个AP裂解酶修复位点这一点也很独特。
