Structural model for covalent adhesion of the Streptococcus pyogenes pilus through a thioester bond

J Biol Chem. 2014 Jan 3;289(1):177-89. doi: 10.1074/jbc.M113.523761. Epub 2013 Nov 12.


The human pathogen Streptococcus pyogenes produces pili that are essential for adhesion to host surface receptors. Cpa, the adhesin at the pilus tip, was recently shown to have a thioester-containing domain. The thioester bond is believed to be important in adhesion, implying a mechanism of covalent attachment analogous to that used by human complement factors. Here, we have characterized a second active thioester-containing domain on Cpa, the N-terminal domain of Cpa (CpaN). Expression of CpaN in Escherichia coli gave covalently linked dimers. These were shown by x-ray crystallography and mass spectrometry to comprise two CpaN molecules cross-linked by the polyamine spermidine following reaction with the thioester bonds. This cross-linked CpaN dimer provides a model for the covalent attachment of Cpa to target receptors and thus the streptococcal pilus to host cells. Similar thioester domains were identified in cell wall proteins of other Gram-positive pathogens, suggesting that thioester domains are more widely used and provide a mechanism of adhesion by covalent bonding to target molecules on host cells that mimics that used by the human complement system to eliminate pathogens.

Keywords: Bacterial Adhesion; Bacterial Pathogenesis; Bacterial Pilus; Crystal Structure; Mass Spectrometry (MS); Post-translational Modification; Protein Cross-linking; Protein Domains; Streptococcus pyogenes; Thioester Domain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adhesins, Bacterial / chemistry*
  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / metabolism
  • Base Sequence
  • Complement System Proteins / chemistry
  • Complement System Proteins / genetics
  • Complement System Proteins / metabolism
  • Crystallography, X-Ray
  • Escherichia coli
  • Fimbriae, Bacterial / chemistry*
  • Fimbriae, Bacterial / genetics
  • Fimbriae, Bacterial / metabolism
  • Humans
  • Models, Molecular*
  • Molecular Sequence Data
  • Protein Multimerization*
  • Protein Structure, Quaternary
  • Protein Structure, Tertiary
  • Streptococcus pyogenes / chemistry*
  • Streptococcus pyogenes / genetics
  • Streptococcus pyogenes / pathogenicity


  • Adhesins, Bacterial
  • Complement System Proteins

Associated data

  • GENBANK/AGQ45688
  • GENBANK/KC622314
  • PDB/4C0Z