Discovery of a novel and rich source of gluten-degrading microbial enzymes in the oral cavity

PLoS One. 2010 Oct 11;5(10):e13264. doi: 10.1371/journal.pone.0013264.

Abstract

Background: Celiac disease is a T cell mediated-inflammatory enteropathy caused by the ingestion of gluten in genetically predisposed individuals carrying HLA-DQ2 or HLA-DQ8. The immunogenic gliadin epitopes, containing multiple glutamine and proline residues, are largely resistant to degradation by gastric and intestinal proteases. Salivary microorganisms however exhibit glutamine endoprotease activity, discovered towards glutamine- and proline-rich salivary proteins. The aim was to explore if gliadins can serve as substrates for oral microbial enzymes.

Methodology/principal findings: Proteolytic activity in suspended dental plaque was studied towards a) gliadin-derived paranitroanilide(pNA)-linked synthetic enzyme substrates b) a mixture of natural gliadins and c) synthetic highly immunogenic gliadin peptides (33-mer of α2-gliadin and 26-mer of γ-gliadin). In addition, gliadin zymography was conducted to obtain the approximate molecular weights and pH activity profiles of the gliadin-degrading oral enzymes and liquid iso-electric focusing was performed to establish overall enzyme iso-electric points. Plaque bacteria efficiently hydrolyzed Z-YPQ-pNA, Z-QQP-pNA, Z-PPF-pNA and Z-PFP-pNA, with Z-YPQ-pNA being most rapidly cleaved. Gliadin immunogenic domains were extensively degraded in the presence of oral bacteria. Gliadin zymography revealed that prominent enzymes exhibit molecular weights >70 kD and are active over a broad pH range from 3 to 10. Liquid iso-electric focusing indicated that most gliadin-degrading enzymes are acidic in nature with iso-electric points between 2.5 and 4.0.

Conclusions/significance: This is the first reported evidence for gluten-degrading microorganisms associated with the upper gastro-intestinal tract. Such microorganisms may play a hitherto unappreciated role in the digestion of dietary gluten and thus protection from celiac disease in subjects at risk.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Chromatography, High Pressure Liquid
  • Enzymes / chemistry
  • Enzymes / metabolism*
  • Gliadin / metabolism
  • Glutens / metabolism*
  • Hydrogen-Ion Concentration
  • Hydrolysis
  • Isoelectric Focusing
  • Molecular Sequence Data
  • Mouth / microbiology*
  • Sequence Homology, Amino Acid
  • Spectrometry, Mass, Electrospray Ionization
  • Tandem Mass Spectrometry

Substances

  • Enzymes
  • Glutens
  • Gliadin