title: Histatin 3-mediated killing of Candida albicans: effect of extracellular salt concentration on binding and internalization.
abstract: Human saliva contains histidine-rich proteins, histatins, which have antifungal activity in vitro. The mechanism by which histatins are able to kill Candida albicans may have clinical significance but is currently unknown. Using radiolabeled histatin 3, we show that the protein binds to C. albicans spheroplasts in a manner that is dependent on time and concentration. Binding to the spheroplasts was saturable and could be competed with unlabeled histatin 3. A single histatin 3 binding site with a K(d) = 5.1 microM was detected. Histatin 3 binding resulted in potassium and magnesium efflux, predominantly within the first 30 min of incubation. Studies with fluorescent histatin 3 demonstrate that the protein is internalized by C. albicans and that translocation of histatin inside the cell is closely associated with cell death. Histatin binding, internalization, and cell death are accelerated in low-ionic-strength conditions. Indeed, a low extracellular salt concentration was essential for cell death to occur, even when histatin 3 was already bound to the cell. The interaction of histatin 3 with C. albicans, and subsequent cell death, is inhibited at low temperature. These results demonstrate that the candidacidal activity of histatin 3 is not due exclusively to binding at the cell surface but also involves subsequent interactions with the cell.
authors.affiliation: Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, Bethesda, Maryland 20892, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
authors.forename: I
authors.initials: I
authors.lastname: Ambudkar
authors.forename: H
authors.initials: H
authors.lastname: Yamagishi
authors.forename: W
authors.initials: W
authors.lastname: Swaim
authors.forename: T J
authors.initials: TJ
authors.lastname: Walsh
authors.forename: B C
authors.initials: BC
authors.lastname: O'Connell
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D002176:Candida albicans / Q000187:drug effects / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D005110:Extracellular Space / Q000737:chemistry; D054808:Histatins; D008274:Magnesium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D013104:Spheroplasts / Q000187:drug effects / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: C068075:HTN3 protein, human; D054808:Histatins; D011506:Proteins; D012965:Sodium Chloride; D008274:Magnesium; D011188:Potassium