San Martin M C, Stamford N P, Dammerova N, Dixon N E, Carazo J M
Centro Nacional de Biotecnología (C.S.I.C.), Universidad Autónoma de Madrid, Cantoblanco, Spain.
J Struct Biol. 1995 May-Jun;114(3):167-76. doi: 10.1006/jsbi.1995.1016.
The DnaB protein is the major replicative DNA helicase in Escherichia coli. It hydrolyzes ATP to promote its translocation in the 5' to 3' direction on single-stranded DNA templates, facilitating the separation of strands of duplex DNA in its path. This places it on the lagging strands at replication forks during chromosomal DNA replication. Electron microscopic images of negatively stained DnaB protein have been studied and processed to produce a three-dimensional reconstruction of the protein oligomer at 2.7 nm resolution. While it is known that the native protein is a complex of six identical 52-kDa subunits, the specimen shows threefold rather than sixfold symmetry, with three outer stain-excluding regions surrounding another six, more massive, lobules. There is a channel through the particle that appears fully open on both sides. Based on these results, a structural model for the oligomer is presented, and functional implications are considered.
DnaB蛋白是大肠杆菌中的主要复制性DNA解旋酶。它水解ATP以促进其在单链DNA模板上沿5'至3'方向移位，从而促进其路径中双链DNA链的分离。这使其在染色体DNA复制期间位于复制叉处的滞后链上。已对负染色的DnaB蛋白的电子显微镜图像进行了研究和处理，以产生分辨率为2.7 nm的蛋白质寡聚体的三维重建。虽然已知天然蛋白是由六个相同的52 kDa亚基组成的复合物，但标本显示出三重而非六重对称性，有三个外部不被染色的区域围绕着另外六个更大的小叶。颗粒中有一个通道，两侧似乎完全开放。基于这些结果，提出了寡聚体的结构模型，并考虑了其功能意义。
