Structural basis of pilus anchoring by the ancillary pilin RrgC of Streptococcus pneumoniae

J Biol Chem. 2014 Jun 13;289(24):16988-97. doi: 10.1074/jbc.M114.555854. Epub 2014 Apr 21.


Pili are surface-attached, fibrous virulence factors that play key roles in the pathogenesis process of a number of bacterial agents. Streptococcus pneumoniae is a causative agent of pneumonia and meningitis, and the appearance of drug-resistance organisms has made its treatment challenging, especially in developing countries. Pneumococcus-expressed pili are composed of three structural proteins: RrgB, which forms the polymerized backbone, RrgA, the tip-associated adhesin, and RrgC, which presumably associates the pilus with the bacterial cell wall. Despite the fact that the structures of both RrgA and RrgB were known previously, structural information for RrgC was still lacking, impeding the analysis of a complete model of pilus architecture. Here, we report the structure of RrgC to 1.85 Å and reveal that it is a three-domain molecule stabilized by two intradomain isopeptide bonds. RrgC does not depend on pilus-specific sortases to become attached to the cell wall; instead, it binds the preformed pilus to the peptidoglycan by employing the catalytic activity of SrtA. A comprehensive model of the type 1 pilus from S. pneumoniae is also presented.

Keywords: Bacterial Adhesion; Bacterial Toxin; Crystal Structure; Infectious Disease; Virulence Factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Aminoacyltransferases / metabolism
  • Bacterial Proteins / metabolism
  • Cysteine Endopeptidases / metabolism
  • Fimbriae Proteins / chemistry*
  • Fimbriae Proteins / genetics
  • Fimbriae Proteins / metabolism
  • Fimbriae, Bacterial / chemistry
  • Fimbriae, Bacterial / metabolism*
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Tertiary
  • Streptococcus pneumoniae / chemistry*
  • Streptococcus pneumoniae / metabolism


  • Bacterial Proteins
  • sortase C
  • Fimbriae Proteins
  • Aminoacyltransferases
  • Cysteine Endopeptidases