The Inner Membrane Protein PilG Interacts with DNA and the Secretin PilQ in Transformation

PLoS One. 2015 Aug 6;10(8):e0134954. doi: 10.1371/journal.pone.0134954. eCollection 2015.

Abstract

Expression of type IV pili (Tfp), filamentous appendages emanating from the bacterial surface, is indispensable for efficient neisserial transformation. Tfp pass through the secretin pore consisting of the membrane protein PilQ. PilG is a polytopic membrane protein, conserved in Gram-positive and Gram-negative bacteria, that is required for the biogenesis of neisserial Tfp. PilG null mutants are devoid of pili and non-competent for transformation. Here, recombinant full-length, truncated and mutated variants of meningococcal PilG were overexpressed, purified and characterized. We report that meningococcal PilG directly binds DNA in vitro, detected by both an electromobility shift analysis and a solid phase overlay assay. PilG DNA binding activity was independent of the presence of the consensus DNA uptake sequence. PilG-mediated DNA binding affinity was mapped to the N-terminus and was inactivated by mutation of residues 43 to 45. Notably, reduced meningococcal transformation of DNA in vivo was observed when PilG residues 43 to 45 were substituted by alanine in situ, defining a biologically significant DNA binding domain. N-terminal PilG also interacted with the N-terminal region of PilQ, which previously was shown to bind DNA. Collectively, these data suggest that PilG and PilQ in concert bind DNA during Tfp-mediated transformation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Cell Membrane / chemistry
  • Cell Membrane / genetics
  • Cell Membrane / metabolism
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / metabolism*
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Fimbriae Proteins / chemistry
  • Fimbriae Proteins / genetics
  • Fimbriae Proteins / metabolism*
  • Fimbriae, Bacterial / chemistry
  • Fimbriae, Bacterial / genetics
  • Fimbriae, Bacterial / metabolism*
  • Gene Expression
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Neisseria meningitidis / genetics
  • Neisseria meningitidis / metabolism*
  • Plasmids / chemistry
  • Plasmids / metabolism
  • Protein Binding
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Transformation, Bacterial

Substances

  • DNA, Bacterial
  • Membrane Proteins
  • Recombinant Proteins
  • pilQ protein, bacteria
  • Fimbriae Proteins

Grants and funding

This work was funded by the Research Council of Norway FRIMEDBIO grant no. 177785 and the Centre of Excellence grant no. 146494 for the Centre for Molecular Biology and Neuroscience (CMBN) to TT. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.