Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91180 Gif-sur-Yvette, France.
Synchrotron SOLEIL, L'Orme des Merisiers, 91192 Gif-sur-Yvette, France.
Acta Crystallogr D Struct Biol. 2023 Feb 1;79(Pt 2):177-187. doi: 10.1107/S2059798323000281. Epub 2023 Feb 6.
During the initiation step of bacterial genome replication, replicative helicases depend on specialized proteins for their loading onto oriC. DnaC and DnaI were the first loaders to be characterized. However, most bacteria do not contain any of these genes, which are domesticated phage elements that have replaced the ancestral and unrelated loader gene dciA several times during evolution. To understand how DciA assists the loading of DnaB, the crystal structure of the complex from Vibrio cholerae was determined, in which two VcDciA molecules interact with a dimer of VcDnaB without changing its canonical structure. The data showed that the VcDciA binding site on VcDnaB is the conserved module formed by the linker helix LH of one monomer and the determinant helix DH of the second monomer. Interestingly, DnaC from Escherichia coli also targets this module onto EcDnaB. Thanks to their common target site, it was shown that VcDciA and EcDnaC could be functionally interchanged in vitro despite sharing no structural similarity. This represents a milestone in understanding the mechanism employed by phage helicase loaders to hijack bacterial replicative helicases during evolution.
在细菌基因组复制的起始步骤中，复制解旋酶依赖于专门的蛋白质才能加载到 oriC 上。DnaC 和 DnaI 是最早被鉴定的加载蛋白。然而，大多数细菌都不含有这些基因，它们是被驯化的噬菌体元件，在进化过程中已经多次取代了祖先和不相关的加载蛋白基因 dciA。为了了解 DciA 如何协助 DnaB 的加载，我们解析了来自霍乱弧菌的复合物晶体结构，其中两个 VcDciA 分子与 VcDnaB 的二聚体相互作用，而不会改变其典型结构。数据表明，VcDnaB 上的 VcDciA 结合位点是由一个单体的连接螺旋 LH 和第二个单体的决定螺旋 DH 形成的保守模块。有趣的是，来自大肠杆菌的 DnaC 也将此模块靶向 EcDnaB。由于它们具有共同的靶位点，因此尽管没有结构相似性，但在体外证明了 VcDciA 和 EcDnaC 可以在功能上互换。这代表了在理解噬菌体解旋酶加载蛋白在进化过程中劫持细菌复制解旋酶所采用的机制方面的一个里程碑。
