Killing of Candida albicans by histatin 5: Cellular uptake and energy requirement

Histatins, a group of histidine-rich proteins in human saliva, exhibit anti microbial activity and are therefore considered to be important in the prev ention of infections in the oral cavity. Although killing of C. albicans by histatins has been extensively studied, little is known about the processe s responsible for this antifungal activity. Recent studies show the require ment of metabolic activity and ATP production for histatin 5 killing activi ty. Therefore, the goal of this study was to investigate the kinetics of hi statin 5 interaction at different temperatures with C. albicans wild type c ells and with respiratory deficient mutants of C. albicans. Synthetic hista tin 5 was labeled with fluorescein-5-isothiocyanate (FITC) and its associat ion with C. albicans cells was followed by epi-fluorescence microscopy and fluorescence confocal microscopy. At 37 degreesC, histatin 5 accumulates in tracellularly, and both killing activity and uptake of unlabeled and FITC-l abeled histatin 5 are time- and concentration-dependent. At 4 degreesC, no killing is observed and FITC-histatin 5 is only associated with the cytopla smic membrane. Internalization and killing activity only occurs after cells are transferred to 37 degreesC. In addition, cellular accumulation of hist atin 5 is concomitant with a moderate alteration of membrane integrity lead ing to the release of UV-absorbing cell components into the medium. The upt ake of histatin 5, the release of UV-absorbing materials and killing of C. albicans are markedly decreased by the respiratory inhibitor sodium azide. Concomitantly, respiratory deficient mutants of C. albicans are also less s usceptible to histatin 5. These results indicated that histatin 5 killing a ctivity could be directly correlated to histatin 5 internalization. Both of these processes are prevented by modulators of cellular metabolic activity .