Polymorphism and double hexamer structure in the archaeal minichromosome maintenance (MCM) helicase from Methanobacterium thermoautotrophicum
Polymorphism and double hexamer structure in the archaeal minichromosome maintenance (MCM) helicase from Methanobacterium thermoautotrophicum
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DOI：
10.1074/jbc.m509760200
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发表时间：
2005-12-09
影响因子：
4.8
通讯作者：
Martín, CS
中科院分区：
文献类型：
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作者：
Gómez-Llorente, Y;Fletcher, RJ;Martín, CS
热自养甲烷杆菌微型染色体维持复合体（mtMCM）是一种细胞复制解旋酶，是研究更复杂的真核MCMs的有用模型。生物化学和晶体学证据表明，mtMCM组装为双六聚体（dHex），但先前的电子显微镜研究仅报道了单七聚体或单六聚体的存在（Pape，T.，Meka，H.，Chen，S.，Vicentini，G.，货车脚跟，M.，和奥内斯蒂，S.（2003）EMBO Rep.4，1079-1083; Yu，X.，VanLook，M.美国，Poplawski，A.，Kelman，Z.，Xiang，T.，泰伊，B。K.，和Egelman，E. H.（2002）EMBO Rep.3，792-797）。在这里，我们提出了第一个三维电子显微镜重建的全长mtMCM dHex，其中两个六聚体通过结构上定义良好的N-末端结构域相互接触。dHex具有明显的侧开口，类似于LTag（大T抗原）的侧通道。6-在相同的mtMCM制备中观察到折叠和7-折叠环，但是我们确定作为双环的组装有利于6-折叠结构。此外，还检测到开环，这表明直接mtMCM加载到DNA上的机制。
Methanobacterium thermoautotrophicum minichromosome maintenance complex (mtMCM), a cellular replicative helicase, is a useful model for the more complex eukaryotic MCMs. Biochemical and crystallographic evidence indicates that mtMCM assembles as a double hexamer (dHex), but previous electron microscopy studies reported only the presence of single heptamers or single hexamers (Pape, T., Meka, H., Chen, S., Vicentini, G., Van Heel, M., and Onesti, S. (2003) EMBO Rep. 4, 1079-1083; Yu, X., VanLoock, M. S., Poplawski, A., Kelman, Z., Xiang, T., Tye, B. K., and Egelman, E. H. (2002) EMBO Rep. 3, 792-797). Here we present the first three-dimensional electron microscopy reconstruction of the full-length mtMCM dHex in which two hexamers contact each other via the structurally well defined N-terminal domains. The dHex has obvious side openings that resemble the side channels of LTag (large T antigen). 6-fold and 7-fold rings were observed in the same mtMCM preparation, but we determined that assembly as a double ring favors 6-fold structures. Additionally, open rings were also detected, which suggests a direct mtMCM loading mechanism onto DNA.