title: Interaction of human salivary mucin MG2, its recombinant N-terminal region and a synthetic peptide with Actinobacillus actinomycetemcomitans.
abstract: The antimicrobial properties of human salivary mucin MG2 against the periodontal pathogen, Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans), were investigated using purified MG2, rNMUC7 (a recombinant polypeptide containing residue 1-144 of MG2) and synthetic peptides PEP1 (residue 1-17) and PEP2 (residue 47-63). MG2 and rNMUC7 bound to A. actinomycetemcomitans strains SUNY75, SUNY465, SUNY523, 652 and JP2 in a liquid phase binding assay. The bactericidal activities of rNMUC7, PEP1 and PEP2 against A. actinomycetemcomitans SUNY523 were examined in a colony forming unit killing assay. The LD50 for rNMUC7 was 9 microM, for PEP2 was 20 microM and PEP1 did not exhibit bactericidal activity. The primary structure of these polypeptides was analyzed and a direct relationship between net positive charge and bactericidal activity was found. Screening of saliva samples from 60 individuals on Western blots probed with an anti-MG2 antibody against PEP2 revealed that a 20 kDa MG2 fragment was present in 66% of subjects and that this fragment was not present in glandular secretions. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of tryptic peptides derived from the 20 kDa fragment confirmed that this fragment contained a portion of the amino terminal region of MG2. The present study showed that the N-terminal region of MG2 and a subdomain within this region are microbicidal against A. actinomycetemcomitans and that a 20 kDa fragment of MG2 occurs in whole saliva. This suggests that cleavage of MG2 in vivo may produce fragments with microbicidal properties and that this may represent a novel mechanism of host defense.
authors.affiliation: Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Liu
authors.forename: Sean A
authors.initials: SA
authors.lastname: Rayment
authors.forename: Rodrigo V
authors.initials: RV
authors.lastname: Soares
authors.forename: Frank G
authors.initials: FG
authors.lastname: Oppenheim
authors.forename: Gwynneth D
authors.initials: GD
authors.lastname: Offner
authors.forename: Paula
authors.initials: P
authors.lastname: Fives-Taylor
authors.forename: Robert F
authors.initials: RF
authors.lastname: Troxler
mesh_terms: D000328:Adult; D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects* / Q000254:growth & development; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015153:Blotting, Western; D015169:Colony Count, Microbial; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007525:Isoelectric Focusing; D013058:Mass Spectrometry; D008875:Middle Aged; D009077:Mucins / Q000138:chemical synthesis / Q000494:pharmacology*; D011485:Protein Binding; D011994:Recombinant Proteins; D012463:Saliva / Q000737:chemistry; D012471:Salivary Proteins and Peptides / Q000138:chemical synthesis / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; C083238:MUC7 protein, human; D009077:Mucins; D011994:Recombinant Proteins; D012471:Salivary Proteins and Peptides