Poly-Gly Region Regulates the Accessibility of Metal Binding Sites in Snake Venom Peptides

Insights into the Chemistry, Structure, and Biological Activity of Human Salivary MUC7 Fragments and Their Cu(II) and Zn(II) Complexes

Mucin 7 (MUC7) is one of the salivary proteins whose role in the innate immune system is widely known, but still, neither its mechanism of action nor the impact of its metal coordination is fully understood. MUC7 and its fragments demonstrate potent antimicrobial activity, serving as a natural defense mechanism for organisms against pathogens. This study delves into the bioinorganic chemistry of MUC7 fragments (L1─EGRERDHELRHRRHHHQSPK; L2─EGRERDHELRHRR; L3─HHHQSPK) and their complexes with Cu(II) and Zn(II) ions. The antimicrobial characteristics of the investigated peptides and their complexes were systematically assessed against bacterial and fungal strains at pH 5.40 and pH 7.40. Our findings highlight the efficacy of these systems against Streptococcus sanguinis, a common oral cavity pathogen. Most interestingly, Zn(II) coordination increased (or triggered) the MUC7 antimicrobial activity, which underscores the pivotal role of metal ion coordination in governing the antimicrobial activity of human salivary MUC7 fragments against S. sanguinis.

Bioinorganic chemistry of shepherin II complexes helps to fight Candida albicans?

The fungal cell wall and cell membrane are an important target for antifungal therapies, and a needle-like cell wall or membrane disruption may be an entirely novel antifungal mode of action. In this work, we show how the coordination of Zn(II) triggers the antifungal properties of shepherin II, a glycine- and histidine-rich antimicrobial peptide from the root of Capsella bursa-pastoris. We analyze Cu(II) and Zn(II) complexes of this peptide using experimental and theoretical methods, such as: mass spectrometry, potentiometry, UV-Vis and CD spectroscopies, AFM imaging, biological activity tests and DFT calculations in order to understand the correlation between their metal binding mode, structure, morphology and biological activity. We observe that Zn(II) coordinates to Shep II and causes a structural change, resulting in fibril formation, what has a pronounced biological consequence - a strong anticandidal activity. This phenomenon was observed neither for the peptide itself, nor for its copper(II) complex. The Zn(II) - shepherin II complex can be considered as a starting point for further anticandidal drug discovery, which is extremely important in the era of increasing antifungal drug resistance.

-HH and -HAAAH motifs act as fishing nets for biologically relevant metal ions in metallopeptides

Histidine are one of the most common residues involved in transition metal ion binding in the active sites of metalloenzymes. In order to mimic enzymatic metal binding sites, it is crucial to understand the basic coordination modes of histidine residues, distributed at different positions in the peptide sequence. We show that: (i) the separation of two histidines has a large effect on complex stability - a sequence with adjusting histidine residues forms more stable complexes with Zn(II) than the one in which the residues are separated, while the contrary is observed for Cu(II) complexes, in which amide nitrogens participate in metal binding. No pronounced effect is observed for Ni(II) complexes, where the amides participate in binding at higher pH; (ii) non-coordinating amino acid residues (basic, acidic and aromatic ones) have a significant impact on complex stability; charged and aromatic residues may enhance Zn(II) binding, while the contrary is observed for the amide-binding Cu(II); (iii) cysteine containing sequences are much more effective Zn(II) and Ni(II) binding motifs at pH above 8, while histidine containing ligands are more suitable for effective Zn(II) and Ni(II) binding at lower pH.

A voltammetric peptide biosensor for Cu2+ metal ion quantification in coffee seeds

A prion-derived copper(II)-binding peptide was assembled onto a gold electrode for the building of a voltammetric biosensor for measuring the Cu2+ metal ion in biological samples. The chosen sequence was H-CVNITKQHTVTTTT-NH2, with an appended cysteine residue for binding to the gold surface as a self-assembled monolayer and a histidine residue as the anchorage point for copper(II) complexation. The biosensor showed a linear range of 10-7 to 10-6 M with an 8.0 × 10-8 M detection limit and a 1.0 × 10-7 M quantification limit, with good precision, trueness, and absence of matrix effect. The quantification of Cu2+ was performed in the presence of other transition metal ions, such as Zn2+, Cd2+, Fe2+, or Ni2+, which indicates the excellent selectivity of the biosensor. When the modified electrode was applied for measuring copper(II) in calcined coffee seeds, a difference in copper amount was observed between two Coffea arabica cultivars that were submitted to a treatment with a copper-based antifungal, showing the applicability of the biosensor in the agricultural field.

Zn(II) Induces Fibril Formation and Antifungal Activity in Shepherin I, An Antimicrobial Peptide from Capsella bursa-pastoris

Shepherin I is a glycine- and histidine-rich antimicrobial peptide from the root of a shepherd's purse, whose antimicrobial activity was suggested to be enhanced by the presence of Zn(II) ions. We describe Zn(II) and Cu(II) complexes of this peptide, aiming to understand the correlation between their metal binding mode, structure, morphology, and biological activity. We observe a logical sequence of phenomena, each of which is the result of the previous one: (i) Zn(II) coordinates to shepherin I, (ii) causes a structural change, which, in turn, (iii) results in fibril formation. Eventually, this chain of structural changes has a (iv) biological consequence: The shepherin I-Zn(II) fibrils are highly antifungal. What is of particular interest, both fibril formation and strong anticandidal activity are only observed for the shepherin I-Zn(II) complex, linking its structural rearrangement that occurs after metal binding with its morphology and biological activity.