Comparative antimicrobial profiles of Histatin 5, Histatin 8, and their copper complexes

Histatins are histidine-rich antimicrobial peptides present in human saliva, with histatin 5 (Hst5) demonstrating the most potent antifungal activity. Previous studies have linked the antifungal properties of histatins, particularly those against Candidaspecies, to their ability to bind metal ions such as Cu(II) and Zn(II). While the antimicrobial activity of some histatins is well established, the role of metal ion coordination in their mechanism of action remains an area of ongoing investigation. This study focuses on histatin 8 (Hst8), a less-explored member of the histatin family, and compares its metal-binding and antimicrobial properties to those of Hst5. Using isothermal titration microcalorimetry (ITC), we examined the interactions of Hst8 with Cu(II), Zn(II), and Ni(II) ions and evaluated its antimicrobial activity against Escherichia coli, Staphylococcus aureus and two Candida albicans strains. Our findings revealed significant differences in copper and zinc binding between Hst5 and Hst8, with both peptides exhibiting distinct antifungal profiles. These results highlight the potential role of metal ion coordination in modulating the antimicrobial efficacy of histatins, providing further insight into their therapeutic potential.