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Multiple oligomeric forms of Escherichia coli DnaB helicase revealed by electrospray ionisation mass spectrometry

Watt, Stephen J; Urathamakul, Thitima; Schaeffer, Patrick; Williams, Neal; Sheil, Margaret; Dixon, Nicholas; Beck, Jennifer

Description

The Escherichia coli DnaB protein (DnaB6) 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 DnaB6 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...[Show more]

dc.contributor.authorWatt, Stephen J
dc.contributor.authorUrathamakul, Thitima
dc.contributor.authorSchaeffer, Patrick
dc.contributor.authorWilliams, Neal
dc.contributor.authorSheil, Margaret
dc.contributor.authorDixon, Nicholas
dc.contributor.authorBeck, Jennifer
dc.date.accessioned2015-12-07T22:42:50Z
dc.identifier.issn0951-4198
dc.identifier.urihttp://hdl.handle.net/1885/24721
dc.description.abstractThe Escherichia coli DnaB protein (DnaB6) 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 DnaB6 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 DnaB6 with DnaC. The DnaB6(DnaC)6 complex (calculated Mr 481164) 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.
dc.publisherJohn Wiley & Sons Inc
dc.sourceRapid Communications in Mass Spectrometry
dc.subjectKeywords: bacterial protein; DnaB helicase; DnaC protein, E coli; Escherichia coli protein; protein subunit; unclassified drug; article; chemistry; electrospray mass spectrometry; enzymology; Escherichia coli; methodology; nanotechnology; protein conformation; Bact
dc.titleMultiple oligomeric forms of Escherichia coli DnaB helicase revealed by electrospray ionisation mass spectrometry
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume21
dc.date.issued2007
local.identifier.absfor060199 - Biochemistry and Cell Biology not elsewhere classified
local.identifier.ariespublicationu4005981xPUB34
local.type.statusPublished Version
local.contributor.affiliationWatt, Stephen J, University of Wollongong
local.contributor.affiliationUrathamakul, Thitima, University of Wollongong
local.contributor.affiliationSchaeffer, Patrick, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationWilliams, Neal, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationSheil, Margaret, University of Wollongong
local.contributor.affiliationDixon, Nicholas, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationBeck, Jennifer, University of Wollongong
local.description.embargo2037-12-31
local.bibliographicCitation.issue2
local.bibliographicCitation.startpage132
local.bibliographicCitation.lastpage140
local.identifier.doi10.1002/rcm.2818
dc.date.updated2015-12-07T11:12:10Z
local.identifier.scopusID2-s2.0-33846201624
CollectionsANU Research Publications

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