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TitleThree-dimensional reconstructions from cryoelectron microscopy images reveal an intimate complex between helicase DnaB and its loading partner DnaC.
Journal, issue, pagesStructure, Vol. 6, Issue 4, Page 501-509, Year 1998
Publish dateApr 15, 1998
AuthorsC San Martin / M Radermacher / B Wolpensinger / A Engel / C S Miles / N E Dixon / J M Carazo /
PubMed AbstractBACKGROUND: DNA helicases play a fundamental role in all aspects of nucleic acid metabolism and defects in these enzymes have been implicated in a number of inherited human disorders. DnaB is the ...BACKGROUND: DNA helicases play a fundamental role in all aspects of nucleic acid metabolism and defects in these enzymes have been implicated in a number of inherited human disorders. DnaB is the major replicative DNA helicase in Escherichia coli and has been used as a model system for studying the structure and function of hexameric helicases. The native protein is a hexamer of identical subunits, which in solution forms a complex with six molecules of the loading protein DnaC. DnaB is delivered from this complex onto the DNA template, with the subsequent release of DnaC. We report here the structures of the DnaB helicase hexamer and its complex with DnaC under a defined set of experimental conditions, as determined by three-dimensional cryoelectron microscopy. It was hoped that the structures would provide insight into the mechanisms of helicase activity.
RESULTS: The DnaB structure reveals that six DnaB monomers assemble as three asymmetric dimers to form a polar, ring-like hexamer. The hexamer has two faces, one displaying threefold and the other sixfold symmetry. The six DnaC protomers bind tightly to the sixfold face of the DnaB hexamer. This is the first report of a three-dimensional structure of a helicase obtained using cryoelectron microscopy, and the first report of the structure of a helicase in complex with a loading protein.
CONCLUSIONS: The structures of the DnaB helicase and its complex with DnaC reveal some interesting structural features relevant to helicase function and to the assembly of the two-protein complex. The results presented here provide a basis for a more complete understanding of the structure and function of these important proteins.
External linksStructure / PubMed:9562559
MethodsEM (single particle)
Resolution34.5 - 42.2 Å
Structure data

EMDB-1022:
Three-dimensional reconstructions from cryoelectron microscopy images reveal an intimate complex between helicase DnaB and its loading partner DnaC.
Method: EM (single particle) / Resolution: 34.5 Å

EMDB-1023:
Three-dimensional reconstructions from cryoelectron microscopy images reveal an intimate complex between helicase DnaB and its loading partner DnaC.
Method: EM (single particle) / Resolution: 42.2 Å

Source
  • Escherichia coli (E. coli)

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