Selective effects of histidine‐rich polypeptides on the aggregation and viability of Streptococcus mutans and Streptococcus sanguis

Abstract

Enriched preparations of histidine-rich polypeptides (HRPs) and isolated HRP pairs (1-2, 3-4 and 5-6) degrade in the presence of fresh autologous whole saliva to a series of low-molecular-weight cationic peptides (HRPs 6a-c and 7). Analysis of the HRPs during degradation indicates that: HRP 1 is not the parent molecule of the HRPs; the HRP pairs do not convert to each other in a cascade-like sequence in saliva; and the HRPs can be separated into 2 groups consisting of HRPs 1-2 and 3-7. Preparations containing HRPs 1-7, 1-2, and 3-7 were obtained by fractionation and separation on Bio-Rex 70, and tested for aggregating and antibacterial effects against Streptococcus mutans BHT, S. mutans GS-5 and Streptococcus sanguis G9B. HRPs 1-2 had significant aggregating effects on all 3 strains but the other HRPs had little to no agglutinating ability. The HRPs did not inhibit the growth of S. sanguis, and HRPs 1-2 enhanced its growth. No growth enhancement by the HRPs was observed for the 2 S. mutans strains. However, significant bacterial inhibition of the S. mutans strains was noted after incubation with HRPs 3-7. The data suggest that the dissimilar effects of HRPs 1-2 and 3-7 may be of importance in the colonization and growth of S. mutans and S. sanguis in vivo.

Does Variability in Salivary Protein Concentrations Influence Oral Microbial Ecology and Oral Health?

“…There is a great diversity of oral species (Marsh and Martin, 1984), and strains within species likewise show great genotypic and phenotypic diversity (Kilian et al, 1989;Rudney and Larson, 1994 mutans, and S. sobrinus do not (Kilian and Nyvad, 1990;Scannapieco et al, 1993;Gwynn and Douglas, 1994). Species variation can also be seen for bacterial interactions with lysozyme, lactoferrin, mucins, PRG, and aPRPs, and strains within species may differ in their interactions with those proteins (Arnold et al, 1980;\aconoetal, 1980;Laible and Germaine, 1982;Gibbons et al, 1991 ;Payne et al, 1991;Murray et al, 1992). In vitro studies of salivary protein interactions with bacteria generally rely on strains cultured in laboratories for many generations, and those strains may show phenotypic differences from fresh clinical isolates.…”

“…Histatins are a family of small cationic proteins produced by acinar cells (MacKay et al, 1984c;Oppenheim et al, 1988;Troxler et al, 1990). They lack any enzymatic activity, but are similar to lysozyme in exerting polycationic effects against some Streptococcus and Candida species (MacKay et al, 1984a;Pollock et al, 1984;Payne et al, 1991;Lai et al, 1992). Mucins are major products of submandibular and sublingual gland mucous cells.…”

Identification of Lys-Pro-Gln as a Novel Cleavage Site Specificity of Saliva-associated Proteases

“…The data were plotted in a linear Lineweaver-Burk plot to obtain the overall kinetic parameters V max and K m , and the theoretical enzyme saturation curves were calculated from the linear equation. To establish the optimum pH of KPQ-pNA cleavage, the pH of 0.5 ml of WS supernatant aliquots was adjusted with either 5 M HCl or 1 M NaOH to pH 4,5,6,7,8,9, and 10 prior to the addition of 85 M KPQ-pNA. Experiments were also carried out in the presence of a series of enzymatic inhibitors (Sigma; see Table 3 for details).…”

“…Nevertheless, multiple studies have established that oral fluid displays abundant proteolytic activity that may represent a hitherto unappreciated physical component of digestive activity. Although the significance of oral fluid proteolysis on the initiation of food digestion has not been fully addressed, its proteolytic effect on salivary proteins is being increasingly recognized (1)(2)(3)(4)(5)(6). Alterations imposed by proteolytic enzymes on the structure and function of resident salivary proteins could have both primary and secondary functional effects.…”

“…These constituents comprise a variety of host and bacterial cells and their products as well as a serumlike gingival crevicular transudate. The nonexocrine compo-nents must contribute substantially to the enzymatic activity of whole saliva given the much lower proteolytic activities of pure salivary glandular secretions (4,6,21,22). Saliva is continuously being secreted (ϳ500 -1500 ml/day), thus providing a steady supply of newly synthesized salivary proteins to the oral cavity.…”