These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Multiple oligomeric forms of Escherichia coli DnaB helicase revealed by electrospray ionisation mass spectrometry.
    Author: Watt SJ, Urathamakul T, Schaeffer PM, Williams NK, Sheil MM, Dixon NE, Beck JL.
    Journal: Rapid Commun Mass Spectrom; 2007; 21(2):132-40. PubMed ID: 17154355.
    Abstract:
    The Escherichia coli DnaB protein (DnaB(6)) is the hexameric helicase that unwinds genomic DNA so it can be copied by the DNA replication machinery. Loading of the helicase onto DNA requires interactions of DnaB(6) with six molecules of its loading partner protein, DnaC. Nano-electrospray ionisation mass spectrometry (nanoESI-MS) of mutant proteins was used to examine the roles of the residues Phe102 (F102) and Asp82 (D82) in the N-terminal domain of DnaB in the assembly of the hexamer. When the proteins were prepared in 1 M ammonium acetate containing magnesium and adenosine triphosphate (ATP) at pH 7.6, both hexameric and heptameric forms of wild-type and F102W, F102E and D82N mutant DnaBs were observed in mass spectra. The spectra of the D82N mutant also showed substantial amounts of a decameric species and small amounts of a dodecamer. In contrast, the F102H DnaB mutant was incapable of forming oligomers of order higher than the hexamer. Thus, although Phe102 is not the only determinant of hexamer assembly, this residue has a role in oligomerisation. NanoESI mass spectra were obtained of mixtures of DnaB(6) with DnaC. The DnaB(6)(DnaC)(6) complex (calculated M(r) 481 164) was observed only when the two proteins were present in equimolar amounts. The data are consistent with cooperative assembly of the complex. ESI mass spectra of mixtures containing DnaC and ATP showed that DnaC slowly hydrolysed ATP to ADP as indicated by ions corresponding to DnaC/ATP and DnaC/ADP complexes. These experiments show that E. coli DnaB can form a heptameric complex and that nanoESI-MS can be used to probe assembly of large (>0.5 MDa) macromolecular complexes.
    [Abstract] [Full Text] [Related] [New Search]