Zinc Binding by Histatin 5 Promotes Fungicidal Membrane Disruption in C. albicans and C. glabrata

Histatin 5 (Hst 5) is an antimicrobial peptide produced in human saliva with antifungal activity for opportunistic pathogen Candida albicans. Hst 5 binds to multiple cations including dimerization-inducing zinc (Zn(2+)), although the function of this capability is incompletely understood. Hst 5 is taken up by C. albicans and acts on intracellular targets under metal-free conditions; however, Zn(2+) is abundant in saliva and may functionally affect Hst 5. We hypothesized that Zn(2+) binding would induce membrane-disrupting pores through dimerization. Through the use of Hst 5 and two derivatives, P113 (AA 4-15 of Hst 5) and Hst 5ΔMB (AA 1-3 and 15-19 mutated to Glu), we determined that Zn(2+) significantly increases killing activity of Hst 5 and P113 for both C. albicans and Candida glabrata. Cell association assays determined that Zn(2+) did not impact initial surface binding by the peptides, but Zn(2+) did decrease cell association due to active peptide uptake. ATP efflux assays with Zn(2+) suggested rapid membrane permeabilization by Hst 5 and P113 and that Zn(2+) affinity correlates to higher membrane disruption ability. High-performance liquid chromatography (HPLC) showed that the higher relative Zn(2+) affinity of Hst 5 likely promotes dimerization. Together, these results suggest peptide assembly into fungicidal pore structures in the presence of Zn(2+), representing a novel mechanism of action that has exciting potential to expand the list of Hst 5-susceptible pathogens.