NMR structure of the N-terminal domain of E. coli DnaB helicase: implications for structure rearrangements in the helicase hexamer.
BACKGROUND
DnaB is the primary replicative helicase in Escherichia coli. Native DnaB is a hexamer of identical subunits, each consisting of a larger C-terminal domain and a smaller N-terminal domain. Electron-microscopy data show hexamers with C6 or C3 symmetry, indicating large domain movements and reversible pairwise association.


RESULTS
The three-dimensional structure of the N-terminal domain of E. coli DnaB was determined by nuclear magnetic resonance (NMR) spectroscopy. Structural similarity was found with the primary dimerisation domain of a topoisomerase, the gyrase A subunit from E. coli. A monomer-dimer equilibrium was observed for the isolated N-terminal domain of DnaB. A dimer model with C2 symmetry was derived from intermolecular nuclear Overhauser effects, which is consistent with all available NMR data.


CONCLUSIONS
The monomer-dimer equilibrium observed for the N-terminal domain of DnaB is likely to be of functional significance for helicase activity, by participating in the switch between C6 and C3 symmetry of the helicase hexamer.
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
J
J
Weigelt
S E
SE
Brown
C S
CS
Miles
N E
NE
Dixon
G
G
Otting
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D017124:Conserved Sequence; D004265:DNA Helicases / Q000737:chemistry*; D053488:DnaB Helicases; D004926:Escherichia coli / Q000201:enzymology*; D009682:Magnetic Resonance Spectroscopy; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment
D001426:Bacterial Proteins; D010446:Peptide Fragments; D004265:DNA Helicases; D053488:DnaB Helicases