The BR domain of PsrP interacts with extracellular DNA to promote bacterial aggregation; structural insights into pneumococcal biofilm formation

Sci Rep. 2016 Sep 1;6:32371. doi: 10.1038/srep32371.

Abstract

The major human pathogen Streptococcus pneumoniae is a leading cause of disease and death worldwide. Pneumococcal biofilm formation within the nasopharynx leads to long-term colonization and persistence within the host. We have previously demonstrated that the capsular surface-associated pneumococcal serine rich repeat protein (PsrP), key factor for biofilm formation, binds to keratin-10 (KRT10) through its microbial surface component recognizing adhesive matrix molecule (MSCRAMM)-related globular binding region domain (BR187-385). Here, we show that BR187-385 also binds to DNA, as demonstrated by electrophoretic mobility shift assays and size exclusion chromatography. Further, heterologous expression of BR187-378 or the longer BR120-378 construct on the surface of a Gram-positive model host bacterium resulted in the formation of cellular aggregates that was significantly enhanced in the presence of DNA. Crystal structure analyses revealed the formation of BR187-385 homo-dimers via an intermolecular β-sheet, resulting in a positively charged concave surface, shaped to accommodate the acidic helical DNA structure. Furthermore, small angle X-ray scattering and circular dichroism studies indicate that the aggregate-enhancing N-terminal region of BR120-166 adopts an extended, non-globular structure. Altogether, our results suggest that PsrP adheres to extracellular DNA in the biofilm matrix and thus promotes pneumococcal biofilm formation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Adhesion*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism*
  • Biofilms / growth & development*
  • Cell Membrane / metabolism
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / metabolism*
  • Furin / metabolism
  • Gene Expression
  • Nucleic Acid Conformation
  • Protein Domains
  • Protein Multimerization
  • Protein Structure, Secondary
  • Scattering, Small Angle
  • Streptococcus pneumoniae / cytology*
  • Streptococcus pneumoniae / metabolism*
  • X-Ray Diffraction

Substances

  • Bacterial Proteins
  • DNA, Bacterial
  • Furin