| Autor: |
Edgerton, Mira, Koshlukova, Svetlana E., Lo, Thomas E., Chrzan, Brian G., Straubinger, Robert M., Raj, Periathamby A. |
| Zdroj: |
Journal of Biological Chemistry; August 1998, Vol. 273 Issue: 32 p20438-20447, 10p |
| Abstrakt: |
Candida albicansis the predominant species of yeast isolated from patients with oral candidiasis, which is frequently a symptom of human immunodeficiency virus infection and is a criterion for staging and progression of AIDS. Salivary histatins (Hsts) are potent in vitroantifungal agents and have great promise as therapeutic agents in humans with oral candidiasis. The molecular mechanisms by which Hsts kill yeast cells are not known. We report here, that unlike other antimicrobial proteins, Hsts do not display lytic activities to lipid membranes, measured by release and dequenching of the fluorescent dye calcein. Analysis of the magnitude and time course of Hst-induced calcein release from C. albicanscells further showed that loss of cell integrity was a secondary effect following cell death, rather than the result of primary disruption of the yeast cell membrane.125I-Hst 5 binding studies indicated that C. albicansexpressed a class of saturable binding sites (KD= 1 μm), numbering 8.6 × 105sites/cell. Both Hst 3 and Hst 4 competed for these binding sites with similar affinities, which is consistent with the micromolar concentration of Hsts required for candidacidal activity. Specific 125I-Hst 5 binding was not detected to C. albicansspheroplasts, which were 14-fold less susceptible to Hst 5 killing, compared with intact cells in candidacidal assays. In overlay experiments, 125I-Hst 5 bound to a 67-kDa protein detected in C. albicans whole cell lysates and crude membrane fractions, but not in the yeast cell wall fraction. Consistent with the overlay data, cross-linking of 125I-Hst 5 toC. albicansresulted in the appearance of a specific 73-kDa125I-Hst 5-containing complex that was not detected in the cell wall. 125I-Hst 5-binding protein of similar size was also observed in susceptible S. cerevisiaestrain TI#20. This is the first description of Hst 5 binding sites on C. albicanswhich mediate cell killing and identification of a 67-kDa yeast Hst 5-binding protein. The binding characteristics of Hst 5 are in agreement with the observed potency of its biological effect and provide crucial information to the use of Hst 5 as a therapeutic agent. The presence of a specific C. albicansHst 5-binding protein provides further insight into the potential mechanism of yeast killing and suggests a basis for differential activity between yeast killing and the nontoxic nature of Hsts to humans. |
| Databáze: |
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