Study of the DnaB:DciA interplay reveals insights into the primary mode of loading of the bacterial replicative helicase.

Nucleic acids research 2021 Jun 21

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Replicative helicases are essential proteins that unwind DNA in front of replication forks. Their loading depends on accessory proteins and in bacteria, DnaC and DnaI are well characterized loaders. However, most bacteria do not express either of these two proteins. Instead, they are proposed to rely on DciA, an ancestral protein unrelated to DnaC/I. While the DciA structure from Vibrio cholerae shares no homology with DnaC, it reveals similarities with DnaA and DnaX, two proteins involved during replication initiation. As other bacterial replicative helicases, VcDnaB adopts a toroid-shaped homo-hexameric structure, but with a slightly open dynamic conformation in the free state. We show that VcDnaB can load itself on DNA in vitro and that VcDciA stimulates this function, resulting in an increased DNA unwinding. VcDciA interacts with VcDnaB with a 3/6 stoichiometry and we show that a determinant residue, which discriminates DciA- and DnaC/I-helicases, is critical in vivo. Our work is the first step toward the understanding of the ancestral mode of loading of bacterial replicative helicases on DNA. It sheds light on the strategy employed by phage helicase loaders to hijack bacterial replicative helicases and may explain the recurrent domestication of dnaC/I through evolution in bacteria. © The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.

Citation

Stéphanie Marsin, Yazid Adam, Claire Cargemel, Jessica Andreani, Sonia Baconnais, Pierre Legrand, Ines Li de la Sierra-Gallay, Adeline Humbert, Magali Aumont-Nicaise, Christophe Velours, Françoise Ochsenbein, Dominique Durand, Eric Le Cam, Hélène Walbott, Christophe Possoz, Sophie Quevillon-Cheruel, Jean-Luc Ferat. Study of the DnaB:DciA interplay reveals insights into the primary mode of loading of the bacterial replicative helicase. Nucleic acids research. 2021 Jun 21;49(11):6569-6586