| Autor: |
Conklin SE; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States., Bridgman EC; Department of Chemistry & Physics, Saint Mary's College , Notre Dame, Indiana 46556, United States., Su Q; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States., Riggs-Gelasco P; Department of Chemistry and Biochemistry, College of Charleston , Charleston, South Carolina 29424, United States., Haas KL; Department of Chemistry & Physics, Saint Mary's College , Notre Dame, Indiana 46556, United States., Franz KJ; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States. |
| Abstrakt: |
The histidine-rich salivary peptides of the histatin family are known to bind copper (Cu) and other metal ions in vitro; however, the details of these interactions are poorly understood, and their implications for in vivo antifungal activity have not been established. Here, we show that the availability of Cu during exposure of Candida albicans to histatin-5 (Hist-5) modulates its antifungal activity. Antifungal susceptibility testing revealed that co-treatment of Hist-5 with Cu improved the EC 50 from ∼5 to ∼1 μM, whereas co-treatment with a high-affinity Cu-specific chelator abrogated antifungal activity. Spectrophotometric titrations revealed two previously unrecognized Cu(I)-binding sites with apparent K d values at pH 7.4, ∼20 nM, and confirmed a high-affinity Cu(II)-binding site at the Hist-5 N-terminus with an apparent K d of ∼8 pM. Evaluation of a series of His-to-Ala full-length and truncated Hist-5 peptides identified adjacent His residues (bis-His) as critical anchors for Cu(I) binding, with the presence of a third ligand revealed by X-ray absorption spectroscopy. On their own, the truncated peptides were ineffective at inhibiting the growth of C. albicans, but treatment with supplemental Cu resulted in EC 50 values down to ∼5 μM, approaching that of full-length Hist-5. The efficacy of the peptides depended on an intact bis-His site and correlated with Cu(I) affinity. Together, these results establish new structure-function relationships linking specific histidine residues with Cu binding affinity and antifungal activity and provide further evidence of the involvement of metals in modulating the biological activity of these antifungal peptides. |
