Distinct quaternary states, intermediates, and autoinhibition during loading of the DnaB-replicative helicase by the phage λP helicase loader.

ABSTRACT: Replicative helicases need loader proteins to assemble at DNA replication origins. Multiple copies of the bacteriophage λP (P) loader bind and load the Escherichia coli DnaB (B) replicative helicase onto single-stranded (ss) DNA from the replication origin. We find that the E. coli DnaB•λP complex exists in two forms: B6P5 and B6P6. In the 2.66 Å cryo-EM structure of B6P5, five λP loader copies form a crown-like shape that tightly grips DnaB. In this complex, the closed, planar DnaB is reconfigured into an open spiral with a large enough breach to allow ssDNA to enter an internal chamber. Transition to the open spiral involves λP-induced changes to the Docking Helix (DH)-Linker Helix (LH) interface. Unexpectedly, one λP chain in B6P5 is positioned across the breach. The disposition of this

SUBMITTER: Shatarupa A 

PROVIDER: S-EPMC12661323 | biostudies-literature | 2025 Nov

REPOSITORIES: biostudies-literature