The type IV secretion protein TraK from the Enterococcus conjugative plasmid pIP501 exhibits a novel fold

Acta Crystallogr D Biol Crystallogr. 2014 Apr;70(Pt 4):1124-35. doi: 10.1107/S1399004714001606. Epub 2014 Mar 21.

Abstract

Conjugative plasmid transfer presents a serious threat to human health as the most important means of spreading antibiotic resistance and virulence genes among bacteria. The required direct cell-cell contact is established by a multi-protein complex, the conjugative type IV secretion system (T4SS). The conjugative core complex spans the cellular envelope and serves as a channel for macromolecular secretion. T4SSs of Gram-negative (G-) origin have been studied in great detail. In contrast, T4SSs of Gram-positive (G+) bacteria have only received little attention thus far, despite the medical relevance of numerous G+ pathogens (e.g. enterococci, staphylococci and streptococci). This study provides structural information on the type IV secretion (T4S) protein TraK of the G+ broad host range Enterococcus conjugative plasmid pIP501. The crystal structure of the N-terminally truncated construct TraKΔ was determined to 3.0 Å resolution and exhibits a novel fold. Immunolocalization demonstrated that the protein localizes to the cell wall facing towards the cell exterior, but does not exhibit surface accessibility. Circular dichroism, dynamic light scattering and size-exclusion chromatography confirmed the protein to be a monomer. With the exception of proteins from closely related T4SSs, no significant sequence or structural relatives were found. This observation marks the protein as a very exclusive, specialized member of the pIP501 T4SS.

Keywords: Enterococcus; antibiotic resistance; conjugative plasmid; pIP501; type IV secretion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Enterococcus faecalis / chemistry*
  • Enterococcus faecalis / genetics
  • Enterococcus faecalis / metabolism
  • Models, Molecular
  • Plasmids / chemistry
  • Plasmids / metabolism*
  • Protein Structure, Tertiary

Substances

  • Bacterial Proteins
  • DNA-Binding Proteins

Associated data

  • PDB/4HIC