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.
Weigelt
J
J
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Brown
S E
SE
Miles
C S
CS
Dixon
N E
NE
Otting
G
G
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