ジャーナル: Nucleic Acids Res / 年: 2015 タイトル: Structural basis for DNA strand separation by a hexameric replicative helicase. 著者: Yuriy Chaban / Jonathan A Stead / Ksenia Ryzhenkova / Fiona Whelan / Ekaterina P Lamber / Alfred Antson / Cyril M Sanders / Elena V Orlova / 要旨: Hexameric helicases are processive DNA unwinding machines but how they engage with a replication fork during unwinding is unknown. Using electron microscopy and single particle analysis we determined ...Hexameric helicases are processive DNA unwinding machines but how they engage with a replication fork during unwinding is unknown. Using electron microscopy and single particle analysis we determined structures of the intact hexameric helicase E1 from papillomavirus and two complexes of E1 bound to a DNA replication fork end-labelled with protein tags. By labelling a DNA replication fork with streptavidin (dsDNA end) and Fab (5' ssDNA) we located the positions of these labels on the helicase surface, showing that at least 10 bp of dsDNA enter the E1 helicase via a side tunnel. In the currently accepted 'steric exclusion' model for dsDNA unwinding, the active 3' ssDNA strand is pulled through a central tunnel of the helicase motor domain as the dsDNA strands are wedged apart outside the protein assembly. Our structural observations together with nuclease footprinting assays indicate otherwise: strand separation is taking place inside E1 in a chamber above the helicase domain and the 5' passive ssDNA strands exits the assembly through a separate tunnel opposite to the dsDNA entry point. Our data therefore suggest an alternative to the current general model for DNA unwinding by hexameric helicases.
Particle picking was carried out automatically using BOXER software. Initial references were prepared using several manually selected protein complex images representing different views.
CTF補正
詳細: frames
最終 再構成
想定した対称性 - 点群: C1 (非対称) / アルゴリズム: OTHER / 解像度のタイプ: BY AUTHOR / 解像度: 23.0 Å / 解像度の算出法: OTHER / ソフトウェア - 名称: Imagic, CTFit, CTFFIND3 / 詳細: Final map was calculated from 500 classes / 使用した粒子像数: 3553