Núñez-Ramírez Rafael, Robledo Yolanda, Mesa Pablo, Ayora Silvia, Alonso Juan Carlos, Carazo José María, Donate Luis Enrique
Department of Macro-molecular Structure, Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain.
J Mol Biol. 2006 Apr 7;357(4):1063-76. doi: 10.1016/j.jmb.2006.01.091. Epub 2006 Feb 9.
Quaternary polymorphism is a distinctive structural feature of the DnaB family of replicative DNA hexameric helicases. The Bacillus subtilis bacteriophage SPP1 gene 40 product (G40P) belongs to this family. Three different quaternary states have been described for G40P homohexamers, two of them with C(3) symmetry, and the other with C(6) symmetry. We present three-dimensional reconstructions of the different architectures of G40P hexamers and a variant lacking the N-terminal domain. Comparison of the G40P and the deletion mutant structures sheds new light on the functional roles of the N and C-terminal domains, at the same time that it allows the direct structural mapping of these domains. Based on this new information, hybrid EM/X-ray models are presented for all the different symmetries. These results suggest that quaternary polymorphism of hexameric helicases may be implicated in the translocation along the DNA.
四级多态性是复制性DNA六聚体解旋酶DnaB家族的一个独特结构特征。枯草芽孢杆菌噬菌体SPP1基因40产物（G40P）属于该家族。已描述了G40P同型六聚体的三种不同四级状态，其中两种具有C(3)对称性，另一种具有C(6)对称性。我们展示了G40P六聚体不同结构以及缺少N端结构域的变体的三维重建。G40P和缺失突变体结构的比较为N端和C端结构域的功能作用提供了新的线索，同时也允许对这些结构域进行直接的结构定位。基于这些新信息，针对所有不同对称性给出了混合电子显微镜/ X射线模型。这些结果表明，六聚体解旋酶的四级多态性可能与沿DNA的易位有关。
