title: Is salivary histatin 5 a metallopeptide?
abstract: Histatins are small histidine-rich salivary polypeptides which exhibit antimicrobial activity against Candida albicans. This antimicrobial activity has been ascribed in part to a high content of basic amino acids. However, unlike most other antimicrobial proteins histatins have a high content of histidine, tyrosine and acidic amino acids known to participate in metal ion coordination. This study was conducted to test whether histatin 5 could bind zinc and copper which are metals present in salivary secretions and whole saliva. Physical binding parameters and spectral properties of zinc- and copper-histatin complexes were investigated in order to obtain direct evidence of these interactions. A spectrophotometric competition assay using the metallochromic indicator murexide showed that histatin 5 dissociates metal indicator complexes containing zinc or copper ions. Absorption spectra of histatin 5 at increasing copper chloride concentrations resulted in higher absorbance in the 230-280 nm wavelength range and this spectral change was saturated at a peptide:metal molar ratio of approx. 1:1. A corresponding band was observed in the visible range of the spectrum with a maximum and molar extinction coefficient corresponding to that of copper binding to an ATCUN motif. Quantitative assessment of zinc and copper binding to histatin 5 using isothermal titration calorimetry revealed at least one high affinity site for each metal, with binding constants of 1.2x10(5) and 2.6x10(7) M(-1), respectively. These results indicate that histatin 5 exhibits metallopeptide-like properties. The precise biological significance of this has not yet been established but histatins may contribute significantly to salivary metal binding capacity.
authors.affiliation: Department of Periodontology and Oral Biology, Boston University Goldman School of Dental Medicine, MA 02118-2392, USA.
authors.forename: H
authors.initials: H
authors.lastname: Gusman
authors.forename: U
authors.initials: U
authors.lastname: Lendenmann
authors.forename: J
authors.initials: J
authors.lastname: Grogan
authors.forename: R F
authors.initials: RF
authors.lastname: Troxler
authors.forename: F G
authors.initials: FG
authors.lastname: Oppenheim
mesh_terms: D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000737:chemistry; D001665:Binding Sites; D002118:Calcium / Q000032:analysis; D002151:Calorimetry; D002614:Chelating Agents / Q000494:pharmacology; D003124:Colorimetry; D003300:Copper / Q000032:analysis* / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D054808:Histatins; D006801:Humans; D008969:Molecular Sequence Data; D009114:Murexide / Q000378:metabolism; D011485:Protein Binding; D012471:Salivary Proteins and Peptides / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D015032:Zinc / Q000032:analysis* / Q000378:metabolism
chemical_list: D000935:Antifungal Agents; D002614:Chelating Agents; C068075:HTN3 protein, human; D054808:Histatins; D012471:Salivary Proteins and Peptides; D009114:Murexide; D003300:Copper; D004492:Edetic Acid; D015032:Zinc; D002118:Calcium