ジャーナル: Cell / 年: 2013 タイトル: The bacterial DnaC helicase loader is a DnaB ring breaker. 著者: Ernesto Arias-Palomo / Valerie L O'Shea / Iris V Hood / James M Berger / 要旨: Dedicated AAA+ ATPases deposit hexameric ring-shaped helicases onto DNA to promote replication in cellular organisms. To understand how loading occurs, we used electron microscopy and small angle X- ...Dedicated AAA+ ATPases deposit hexameric ring-shaped helicases onto DNA to promote replication in cellular organisms. To understand how loading occurs, we used electron microscopy and small angle X-ray scattering (SAXS) to determine the ATP-bound structure of the intact E. coli DnaB⋅DnaC helicase/loader complex. The 480 kDa dodecamer forms a three-tiered assembly, in which DnaC adopts a spiral configuration that remodels N-terminal scaffolding and C-terminal motor regions of DnaB to produce a clear break in the helicase ring. Surprisingly, DnaC's AAA+ fold is dispensable for ring remodeling because the DnaC isolated helicase-binding domain can both load DnaB onto DNA and increase the efficiency by which the helicase acts on substrates in vitro. Our data demonstrate that DnaC opens DnaB by a mechanism akin to that of polymerase clamp loaders and indicate that bacterial replicative helicases, like their eukaryotic counterparts, possess autoregulatory elements that influence how hexameric motor domains are loaded onto and unwind DNA.
The particles were selected using DoG picker as available in APPION. The contrast transfer function of the microscope for each micrograph was estimated using CTFFIND3 and phase-flipped using SPIDER. DnaBC particles were subjected to a multi-model refinement as implemented in SPARX using the 3D averages obtained from the RCT reconstructions as initial references.
CTF補正
詳細: Each micrograph
最終 再構成
想定した対称性 - 点群: C3 (3回回転対称) / アルゴリズム: OTHER / 解像度のタイプ: BY AUTHOR / 解像度: 25.0 Å / 解像度の算出法: FSC 0.5 CUT-OFF / ソフトウェア - 名称: EMAN2, SPARX / 使用した粒子像数: 9617