Evaluation of the metal binding properties of the histidine-rich antimicrobial peptides histatin 3 and 5 by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to investigate metal ion interactions with salivary peptides histatin 3 (H3) and histatin 5 (H5), Conformational changes of these peptides in the presence of metal ions were studied using circular dichroism spectroscopy. H3 and H5 formed high affinity complexes with Cu2+ and Ni2+ and, to a lesser extent, with Zn2+. Both peptides show the potential for multiple binding sites for Cu2+ and Ni2+ and only a single strong binding site for Zn2+. The binding of a third Cu2+ ion to H3 seems to enable the binding of a fourth ion to H3. The binding of a second and third Ni2+ ion to H5 has a similar effect in enabling the binding of a fourth ion. None of the metal ions examined stabilized a regular secondary structure for either peptide, Subtle changes in overall conformation are seen with the addition of Cu2+ to both H3 and H5. Copyright (C) 2000 John Wiley & Sons, Ltd.