Pellicle precursor proteins: Acidic proline-rich proteins, statherin, and histatins, and their crosslinking reaction by oral transglutaminase

Previous studies have demonstrated that whole saliva and pellicle formed in vitro from oral fluid contain covalently crosslinked salivary proteins. Th e purpose of this study was to determine which salivary proteins can act as substrates for transglutaminase, an enzyme responsible for the covalent cr osslink reaction between a glutamine residue and a lysine residue. Transglu taminase was prepared from the pellet fraction of human whole saliva. Dansy l cadaverine (N-dansyl-1,5-diaminopentane) was us ed to study the reactivit y of glutamine residues in acidic large and small proline-rich proteins, st atherin, and the major histatins, whereas a glutamine-containing dansylated peptide was used to study the reactivity of lysine residues in these prote ins. Crosslink formation was measured fluorometrically after the addition o f fluorescent probe to the salivary protein substrate and transglutaminase. The covalent attachment of the fluorescent probe to salivary proteins was confirmed by SDS-PAGE. It was found that almost all of the lysines present in the acidic PRPs and statherin, and some of the lysines present in histat ins, could participate in the crosslink reaction. Glutamine reactivity was also observed, but a maximum of only 14% of glutamine residues present in a cidic PRPs and statherin participated in the crosslink formation. These res ults demonstrate that primary pellicle precursor proteins, acidic proline-r ich proteins, statherin, and the major histatins are capable of undergoing crosslink reactions catalyzed by oral transglutaminase. This may enable oth er proteins in the oral cavity to be incorporated into the acquired enamel pellicle.