title: Identification of Rothia bacteria as gluten-degrading natural colonizers of the upper gastro-intestinal tract.
abstract: BACKGROUND
  Gluten proteins, prominent constituents of barley, wheat and rye, cause celiac disease in genetically predisposed subjects. Gluten is notoriously difficult to digest by mammalian proteolytic enzymes and the protease-resistant domains contain multiple immunogenic epitopes. The aim of this study was to identify novel sources of gluten-digesting microbial enzymes from the upper gastro-intestinal tract with the potential to neutralize gluten epitopes.
  
  
  RESULTS
  Oral microorganisms with gluten-degrading capacity were obtained by a selective plating strategy using gluten agar. Microbial speciations were carried out by 16S rDNA gene sequencing. Enzyme activities were assessed using gliadin-derived enzymatic substrates, gliadins in solution, gliadin zymography, and 33-mer α-gliadin and 26-mer γ-gliadin immunogenic peptides. Fragments of the gliadin peptides were separated by RP-HPLC and structurally characterized by mass spectrometry. Strains with high activity towards gluten were typed as Rothia mucilaginosa and Rothia aeria. Gliadins (250 µg/ml) added to Rothia cell suspensions (OD(620) 1.2) were degraded by 50% after ∼30 min of incubation. Importantly, the 33-mer and 26-mer immunogenic peptides were also cleaved, primarily C-terminal to Xaa-Pro-Gln (XPQ) and Xaa-Pro-Tyr (XPY). The major gliadin-degrading enzymes produced by the Rothia strains were ∼70-75 kDa in size, and the enzyme expressed by Rothia aeria was active over a wide pH range (pH 3-10).
  
  
  CONCLUSIONS
  While the human digestive enzyme system lacks the capacity to cleave immunogenic gluten, such activities are naturally present in the oral microbial enzyme repertoire. The identified bacteria may be exploited for physiologic degradation of harmful gluten peptides.
authors.affiliation: Department of Periodontology and Oral Biology, Boston University Henry M. Goldman School of Dental Medicine, Boston, Massachusetts, United States of America.
authors.forename: Maram
authors.initials: M
authors.lastname: Zamakhchari
authors.forename: Guoxian
authors.initials: G
authors.lastname: Wei
authors.forename: Floyd
authors.initials: F
authors.lastname: Dewhirst
authors.forename: Jaeseop
authors.initials: J
authors.lastname: Lee
authors.forename: Detlef
authors.initials: D
authors.lastname: Schuppan
authors.forename: Frank G
authors.initials: FG
authors.lastname: Oppenheim
authors.forename: Eva J
authors.initials: EJ
authors.lastname: Helmerhorst
mesh_terms: D000595:Amino Acid Sequence; D000814:Aniline Compounds / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D003773:Dental Plaque / Q000382:microbiology; D005903:Gliadin / Q000737:chemistry / Q000378:metabolism; D005983:Glutens / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008835:Micrococcaceae / Q000145:classification / Q000201:enzymology / Q000302:isolation & purification* / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D059748:Proteolysis; D012463:Saliva / Q000382:microbiology; D012996:Solutions; D013379:Substrate Specificity; D041742:Upper Gastrointestinal Tract / Q000382:microbiology*
chemical_list: D000814:Aniline Compounds; D010446:Peptide Fragments; D012996:Solutions; C008625:nitroaniline; D005983:Glutens; D005903:Gliadin