Absence of capsule reveals glycan-mediated binding and recognition of salivary mucin MUC7 by Streptococcus pneumoniae

Mol Oral Microbiol. 2016 Apr;31(2):175-88. doi: 10.1111/omi.12113. Epub 2015 Aug 17.


Salivary proteins modulate bacterial colonization in the oral cavity and interact with systemic pathogens that pass through the oropharynx. An interesting example is the opportunistic respiratory pathogen Streptococcus pneumoniae that normally resides in the nasopharynx, but belongs to the greater Mitis group of streptococci, most of which colonize the oral cavity. Streptococcus pneumoniae also expresses a serine-rich repeat (SRR) adhesin, PsrP, which is a homologue to oral Mitis group SRR adhesins, such as Hsa of Streptococcus gordonii and SrpA of Streptococcus sanguinis. As the latter bind to salivary glycoproteins through recognition of terminal sialic acids, we wanted to determine whether S. pneumoniae also binds to salivary proteins through possibly the same mechanism. We found that only a capsule-free mutant of S. pneumoniae TIGR4 binds to salivary proteins, most prominently to mucin MUC7, but that this binding was not mediated through PsrP or recognition of sialic acid. We also found, however, that PsrP is involved in agglutination of human red blood cells (RBCs). After removal of PsrP, an additional previously masked lectin-like adhesin activity mediating agglutination of sialidase-treated RBCs becomes revealed. Using a custom-spotted glycoprotein and neoglycoprotein dot blot array, we identify candidate glycan motifs recognized by PsrP and by the putative S. pneumoniae adhesin that could perhaps be responsible for pneumococcal binding to salivary MUC7 and glycoproteins on RBCs.

Keywords: bacterial lectins; saliva; salivary proteins; serine-rich repeat adhesins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adhesins, Bacterial / genetics
  • Adhesins, Bacterial / metabolism
  • Antigens, Bacterial / immunology
  • Antigens, Bacterial / metabolism
  • Bacterial Adhesion / physiology
  • Bacterial Capsules / metabolism*
  • Hemagglutination / immunology
  • Humans
  • Immobilized Proteins
  • Membrane Proteins / immunology
  • Membrane Proteins / metabolism
  • Mouth / microbiology
  • Mucins / immunology
  • Mucins / metabolism*
  • Mutation
  • N-Acetylneuraminic Acid / metabolism
  • Nasopharynx / microbiology
  • Salivary Proteins and Peptides / immunology
  • Salivary Proteins and Peptides / metabolism*
  • Streptococcus pneumoniae / genetics
  • Streptococcus pneumoniae / immunology
  • Streptococcus pneumoniae / metabolism*
  • Streptococcus sanguis / genetics
  • Streptococcus sanguis / immunology
  • Streptococcus sanguis / metabolism


  • Adhesins, Bacterial
  • Antigens, Bacterial
  • Immobilized Proteins
  • MUC7 protein, human
  • Membrane Proteins
  • Mucins
  • Salivary Proteins and Peptides
  • N-Acetylneuraminic Acid