Salivary histatin 5 (Hst 5) kills the fungal pathogen C. albicans via a mechanism that involves binding and subsequent efflux of cellular ATP. Our aims were to identify inorganic ions found in saliva that influence Hst 5 fungicidal activity. Increasing ionic strength with relevant salivary anions (Cl− and CO3−) did not reduce Hst 5 binding or uptake by yeast cells, but reduced the Hst-induced efflux of ATP. Extracellular MgCl2 (25 mM) maximally inhibited 30–40% of Hst 5 killing with 40% reduction in ATP efflux, while pre-treatment of cells with only 2 mM CaCl2 inhibited 80–90% of killing, and prevented ATP efflux. Loss of fungicidal activity by the addition of CaCl2 or MgCl2 was a result of inhibition of binding of Hst 5 to C. albicans cells. Calcium is a potent inhibitor of Hst 5 candidacidal activity at physiological concentrations and may be the primary salivary ion responsible for the masking effect of saliva.
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References
1.
Baev D, Li X, Edgerton M -2001-. Genetically engineered human salivary histatin genes are functional in Candida albicans: development of a new system for studying histatin candidacidal activity. Microbiology147:3323–3334.
2.
Baron A, DeCarlo A, Featherstone J -1999-. Functional aspects of the human salivary cystatins in the oral environment. Oral Dis5:234–240.
3.
Cannon RD, Holmes AR, Mason AB, Monk BC -1995-. Oral Candida: clearance, colonization or candidiasis? J Dent Res74:1152–1161.
4.
Dawes C -1996-. Factors influencing salivary flow rate and composition. In: Saliva and oral health. Edgar WM, O’Mullane DM, editors. Great Britain: Thanet Press, pp. 38–41.
5.
Edgerton M, Koshlukova SE, Lo TE, Chrzan BG, Straubinger RM, Raj PA -1998-. Candidacidal activity of salivary histatins. Identification of a histatin 5-binding protein on Candida albicans. J Biol Chem273:20438–20447.
6.
Epstein JB, Polsky B -1998-. Oropharyngeal candidiasis: a review of its clinical spectrum and current therapies. Clin Ther20:40–57.
7.
Ferguson DB -1989-. Salivary electrolytes. In: Human saliva: clinical chemistry and microbiology. Tenovuo JO, editor. Boca Raton: CRC Press, pp. 75–100.
8.
Flora B, Helmerhorst EJ, Gusman H, Troxler RF, Oppenheim FG -2002-. Assessment of the factors that mask the fungicidal activity of parotid saliva -abstract-. J Dent Res81-Spec Iss A-:1800.
9.
Grogan J, McKnight CJ, Troxler RF, Oppenheim FG -2001-. Zinc and copper bind to unique sites of histatin 5. FEBS Lett23:76–80.
10.
Gusman H, Lendenmann U, Grogan J, Troxler RF, Oppenheim FG -2001-. Is salivary histatin 5 a metallopeptide? Biochim Biophys Acta1545:86–95.
11.
Hay DI, Moreno EC -1989-. Statherin and acidic proline-rich proteins. In: Human saliva: clinical chemistry and microbiology. Tenovuo JO, editor. Boca Raton: CRC Press, pp. 131–150.
12.
Helmerhorst EJ, van’t Hof W, Breeuwer P, Veerman EC, Abee T, Troxler RF, et al. -2001-. Characterization of histatin 5 with respect to amphipathicity, hydrophobicity, and effects on cell and mitochondrial membrane integrity excludes a candidacidal mechanism of pore formation. J Biol Chem276:5643–5649.
13.
Koshlukova SE, Lloyd TL, Araujo MW, Edgerton M -1999-. Salivary histatin 5 induces non-lytic release of ATP from Candida albicans leading to cell death. J Biol Chem274:18872–18879.
14.
Koshlukova SE, Araujo MW, Baev D, Edgerton M -2000-. Released ATP is an extracellular cytotoxic mediator in salivary histatin 5-induced killing of Candida albicans. Infect Immun68:6848–6856.
15.
Larsen MJ, Jensen AF, Madsen DM, Pearce EIF -1999-. Individual variations of pH, buffer capacity and concentrations of calcium and phosphate in unstimulated whole saliva. Arch Oral Biol44:111–117.
16.
Madapallimattam G, Bennick A -1990-. Phosphopeptides derived from human salivary acidic proline-rich proteins. Biological activities and concentration in saliva. Biochem J270:297–304.
17.
Matsuo S, Lagerlöf F -1991-. Relationship between total and ionized calcium concentrations in human whole saliva and dental plaque fluid. Arch Oral Biol36:525–527.
18.
Oppenheim FG, Yang YC, Diamond RD, Hyslop D, Offner GD, Troxler RF -1986-. The primary structure and functional characterization of the neutral histidine-rich polypeptide from human parotid secretion. J Biol Chem261:1177–1182.
19.
Oppenheim FG, Xu T, McMillian FM, Levitz SM, Diamond RD, Offner GD, et al. -1988-. Histatins, a novel family of histidine-rich proteins in human parotid secretion. Isolation, characterization, primary structure, and fungistatic effects on Candida albicans. J Biol Chem263:7472–7477.
20.
Xu T, Levitz MS, Diamond RD, Oppenheim FG -1991-. Anticandidal activity of major human salivary histatins. Infect Immun70:2549–2554.
21.
Xu Y, Ambudkar I, Yamagishi H, Swaim W, Walsh TJ, O’Connell BC -1999-. Histatin 3-mediated killing of Candida albicans: effect of extracellular salt concentration on binding and internalization. Antimicrob Agents Chemother43:2256–2262.
