Zn(II) Affinity and Structural Conformations of 2His-2Cys Zinc Finger-Like Motif Peptide Determined by Ion Mobility–Mass Spectrometry and PM6 Molecular Modeling

This study focuses on investigating the conformational structure and zinc(II) affinity of a zinc finger-like motif (ZFM) peptide with the sequence acetyl-His₁-Cys₂-Gly₃-Pro₄-Gly₅-His₆-Cys₇, where bold highlights the potential zinc(II) binding sites. Zinc fingers are crucial protein motifs known for their high specificity and affinity for zinc ions. The ZFM peptide's sequence contains the 2His-2Cys zinc-binding sites similar to those in natural zinc finger proteins but without the hydrophobic core, making it a valuable model for studying zinc(II)–peptide interactions. Previous research on related peptides showed that collision cross sections and B3LYP modeling predicted that the His-2Cys-carboxyl terminus coordination of zinc(II) was more stable than the 2His-2Cys. Employing a comprehensive approach integrating ion mobility–mass spectrometry and theoretical modeling techniques, various zinc(II) binding modes of the ZFM have been thoroughly compared to ascertain their influence on the competitive threshold collision-induced dissociation method for measuring the relative gas-phase Zn(II) affinity of the ZFM peptide. The measured Zn(II) affinity of ZFM is greater than those measured recently for two peptides with similar primary structures, acetyl-His₁-Cys₂-Gly₃-Pro₄-Gly₅-Gly₆-Cys₇ and acetyl-Asp₁-His₂-Gly₃-Pro₄-Gly₅-Gly₆-Cys₇, indicating the preference for the His₁-Cys₂-His₆-Cys₇ side groups for coordinating zinc(II) over the His-2Cys-carboxyl terminus or Asp-His-Cys-carboxyl terminus in these related heptapeptides.