title: A structural model for the Escherichia coli DnaB helicase based on electron microscopy data.
abstract: The DnaB protein is the major replicative DNA helicase in Escherichia coli. It hydrolyzes ATP to promote its translocation in the 5' to 3' direction on single-stranded DNA templates, facilitating the separation of strands of duplex DNA in its path. This places it on the lagging strands at replication forks during chromosomal DNA replication. Electron microscopic images of negatively stained DnaB protein have been studied and processed to produce a three-dimensional reconstruction of the protein oligomer at 2.7 nm resolution. While it is known that the native protein is a complex of six identical 52-kDa subunits, the specimen shows threefold rather than sixfold symmetry, with three outer stain-excluding regions surrounding another six, more massive, lobules. There is a channel through the particle that appears fully open on both sides. Based on these results, a structural model for the oligomer is presented, and functional implications are considered.
authors.affiliation: Centro Nacional de Biotecnología (C.S.I.C.), Universidad Autónoma de Madrid, Cantoblanco, Spain.
authors.forename: M C
authors.initials: MC
authors.lastname: San Martin
authors.forename: N P
authors.initials: NP
authors.lastname: Stamford
authors.forename: N
authors.initials: N
authors.lastname: Dammerova
authors.forename: N E
authors.initials: NE
authors.lastname: Dixon
authors.forename: J M
authors.initials: JM
authors.lastname: Carazo
mesh_terms: D001426:Bacterial Proteins; D002850:Chromatography, Gel; D003196:Computer Graphics; D004265:DNA Helicases / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure; D053488:DnaB Helicases; D004926:Escherichia coli / Q000201:enzymology*; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D008968:Molecular Conformation; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D004265:DNA Helicases; D053488:DnaB Helicases