The DnaB.DnaC complex: a structure based on dimers assembled around an occluded channel.
Replicative helicases are motor proteins that unwind DNA at replication forks. Escherichia coli DnaB is the best characterized member of this family of enzymes. We present the 26 A resolution three-dimensional structure of the DnaB hexamer in complex with its loading partner, DnaC, obtained from cryo-electron microscopy. Analysis of the volume brings insight into the elaborate way the two proteins interact, and provides a structural basis for control of the symmetry state and inactivation of the helicase by DnaC. The complex is arranged on the basis of interactions among DnaC and DnaB dimers. DnaC monomers are observed for the first time to arrange as three dumb-bell-shaped dimers that interlock into one of the faces of the helicase. This could be responsible for the freezing of DnaB in a C(3) architecture by its loading partner. The central channel of the helicase is almost occluded near the end opposite to DnaC, such that even single-stranded DNA could not pass through. We propose that the DnaB N-terminal domain is located at this face.
Bárcena
M
M
Centro Nacional de Biotecnología (CSIC), Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Ruiz
T
T
Donate
L E
LE
Brown
S E
SE
Dixon
N E
NE
Radermacher
M
M
Carazo
J M
JM
D001426:Bacterial Proteins / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D004265:DNA Helicases / Q000648:ultrastructure*; D004261:DNA Replication; D019281:Dimerization; D053488:DnaB Helicases; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D007091:Image Processing, Computer-Assisted; D008961:Models, Structural; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000648:ultrastructure
D001426:Bacterial Proteins; C071702:DnaC protein, E coli; D029968:Escherichia coli Proteins; C083184:MocB protein, Bacteroides fragilis; D011994:Recombinant Proteins; D004265:DNA Helicases; D053488:DnaB Helicases