Zn(II)-alloferon complexes - Similar sequence, different coordination modes, no antibacterial activity

Often, in the search for a highly defined scientific phenomenon, a different one becomes apparent. This was also the case of this work, in the scope of which we planned to search for metal-enhanced, novel antibacterial/antifungal compounds. Instead, we denied the existence of such and revealed the details of the bioinorganic chemistry of Zn(II)-alloferon complexes. Zinc(II) complexes of alloferon 1 and 2, ligands with a sequential difference of one amino acid only, show a substantially different coordination pattern at physiological pH. In the case of Zn(II)-alloferon 1 species, a histamine-like binding mode is observed (N-terminal amine and imidazole of His-1) and the coordination sphere is completed with the imidazole nitrogens of His-6 and His-9; His-12 is not involved in binding. In the case of Zn(II)-alloferon 2, the N-terminal amine and all the three imidazoles present in the sequence participate in the coordination, however, with the chemical shift of His-5 being less affected than those of other imidazoles. The histamine-like binding in Zn(II)-alloferon 1 complex strongly enhances its thermodynamic stability in comparison to the His-1 lacking alloferon 2 analogue. Despite previous reports on the antibacterial and antifungal activity of alloferon 1, no such activity was detected, neither for alloferon 1 and 2 nor for their Zn(II) complexes.

Cu(II) complexes with peptides from FomA protein containing -His-Xaa-Yaa-Zaa-His and -His-His-motifs. ROS generation and DNA degradation

Mono- and dinuclear Cu(II) complexes with Ac-PTVHNEYH-NH₂ (L1) and Ac-NHHTLND-NH₂ (L2) peptides from FomA protein of Fusobacterium nucleatum were studied by potentiometry, spectroscopic methods (UV-Vis, CD, EPR) and MS technique. The dominant mononuclear complexes for L1 ligand are: CuHL (pH range 5.0-6.0) with 2N {2N_im}, CuH_-2L (pH range 8.0-8.5) and CuH_-3L species (above pH 9.0) with 4N {N_im, 3N^-} coordination modes. The complexes: CuH_-1L with 3N {2N_im, N^-}, CuH_-2L with 3N {N_im, 2N^-} and CuH_-3L with 4N {N_im, 3N^-} binding sites are proposed for the L2 ligand. Probably in the CuH_-2L complex for CuL2 system the second His residue in His-His sequence is bound to Cu(II) ion, while the first His residue may stabilize this complex by His-His and/or His-Cu(II) interactions. The dominant dinuclear Cu₂L1 complexes in the pH range 6.5-10.5 are: the Cu₂H_-4L and Cu₂H_-6L species with 3N{N_im, 2N^-}4N{N_im, 3N^-} and 4N{N_im, 3N^-}4N{N_im, 3N^-} binding sites, respectively. In the case of the Cu₂L2 complex in the pH range 7.2-10.5, the Cu₂H_-4L and Cu₂H_-7L species dominate with 2N{N_im, N^-}4N{N_im, 3N^-} and (Cu(OH)₄^2-4N{N_im, 3N^-}) coordination modes, respectively. The ability to generate reactive oxygen species (ROS) by uncomplexed Cu(II) ions, ligands and their complexes at pH 7.4 in the presence of hydrogen peroxide or ascorbic acid was studied. UV-Vis, luminescence, EPR spin trapping and gel electrophoresis methods were used. Both complexes produce higher level of ROS compared to those of their ligands. ROS produced by Cu(II) complexes are hydroxyl radical and singlet oxygen, which contribute to oxidative DNA cleavage.

Copper(ii) complexes with alloferon analogues containing phenylalanine H6F and H12F stability and biological activity lower stabilization of complexes compared to analogues containing tryptophan

Copper(ii) complex formation processes between alloferon 1 (Allo1) (H1 GVSGH6 GQH9 GVH12G) analogues where the phenylalanine residue is introduced in the place of His residue H6F and H12F have been studied by potentiometric, UV-visible, CD and EPR spectroscopic, and MS methods. For the phenylalanine analogues of alloferon 1, complex speciation has been obtained for a 1 : 1, 2 : 1 and 3 : 1 metal-to-ligand molar ratio. At physiological pH and in 1 : 1 metal-to-ligand molar ratio the phenylalanine analogues of alloferon 1 form a CuL complex similar to that of alanine analogues with the 4N{NH2,N1Im,2NIm} coordination mode. The stability of the complexes of the phenylalanine analogues is higher in comparison to those of alanine analogues, but lower in comparison to those containing tryptophan. Injection of Allo12F into insects induced prominent apoptotic changes in all hemocytes. The presence of apoptotic bodies only in the insect hemolymph testifies to the fact that Allo12F is an extremely pro-apoptotic peptide.

Copper complexes of synthetic peptides mimicking neurotrophin-3 enhance neurite outgrowth and CREB phosphorylation

In this work we report on the synthesis and physiochemical/biological characterization of a peptide encompassing the first thirteen residues of neurotrophin-3 (NT-3). The protein capability to promote neurite outgrowth and axonal branching by a downstream mechanism that involves the increase of the cAMP response element-binding level (CREB) was found for the NT3(1-13) peptide, thus validating its protein mimetic behaviour. Since copper ions are also involved in neurotransmission and their internalization may be an essential step in neuron differentiation and CREB phosphorylation, the peptide and its copper complexes were characterized by potentiometric and spectroscopic techniques, including UV-visible, CD and EPR. To have a detailed picture of the coordination features of the copper complexes with NT3(1-13), we also scrutinized the two peptide fragments encompassing the shorter sequences 1-5 and 5-13, respectively, showing that the amino group is the main anchoring site for Cu(ii) at physiological pH. The peptide activity increased in the presence of copper ions. The effect of copper(ii) addition is more marked for NT3(1-13) than the other two peptide fragments, in agreement with its higher affinity for metal ions. Confocal microscopy measurements carried out on fluorescently labelled NT3(1-13) indicated that copper ions increase peptide internalization.

Stability of Cu(ii) complexes with FomA protein fragments containing two His residues in the peptide chain

The coordination process of Cu(ii) ions with FomA protein fragments ofFusobacterium nucleatumcontaining two histydyl residues was determined.

Copper ion interaction with the RNase catalytic site fragment of the angiogenin protein: an experimental and theoretical investigation

The angiogenin protein (Ang) is a member of the vertebrate-specific secreted ribonucleases and one of the most potent angiogenic factors known. Ang is a normal constituent of human plasma and its concentration increases under some physiological and pathological conditions to promote neovascularization. Ang was originally identified as an angiogenic tumour factor, but its biological activity has been found to extend from inducing angiogenesis to promoting cell survival in different neurodegenerative diseases. Ang exhibits weak ribonucleolytic activity, which is critical for its biological functions. The RNase catalytic sites are two histidine residues, His-13 and His-114, and the lysine Lys-40. Copper is also an essential cofactor in angiogenesis and influences angiogenin's biological properties. The main Cu(ii) anchoring site of Ang is His-114, where metal binding inhibits RNase activity of the protein. To reveal the Cu(ii) coordination environment in the C-terminal domain of the Ang protein, we report on the characterization, by means of potentiometric, voltammetric, and spectroscopic (CD, UV-Vis and EPR) methods and DFT calculations, of Cu(ii) complexes formed with a peptide fragment including the Ang sequence 112-117 (PVHLDQ). Potentiometric titrations indicated that [CuLH_-2] is the predominant species at physiological pH. EPR, voltammetric data and DFT calculations are consistent with a CuN₃O₂ coordination mode in which a distorted square pyramidal arrangement of the peptide was observed with the equatorial positions occupied by the nitrogen atoms of the deprotonated amides of the Asp and Leu residues, the δ-N atom of histidine and the oxygen atom of the aspartic carboxylic group. Moreover, two analogous peptides encompassing the PVHLNQ and LVHLDQ sequences were also characterized by using thermodynamic, spectroscopic and DFT studies to reveal the role they play in Cu(ii) complex formation by the carboxylate side chain of the Asp and Pro residues, a known breaking-point in metal coordination.

Relationship between copper(ii) complexes with FomA adhesin fragments ofF. nucleatumand colorectal cancer. Coordination pattern and ability to promote ROS production

The copper(ii) binding of the fragments of FomA was studied. Complexes stimulate the CT26 cell line to produce ROS which lead to oxidative stress.

High stability and biological activity of the copper(II) complexes of alloferon 1 analogues containing tryptophan

Copper(II) complex formation processes between the alloferon 1 (Allo1) (HGVSGHGQHGVHG) analogues where the tryptophan residue is introducing in the place His residue H1W, H6W, H9W and H12W have been studied by potentiometric, UV-visible, CD and EPR spectroscopic, and MS methods. For all analogues of alloferon 1 complex speciation have been obtained for a 1:1 metal-to-ligand molar ratio and 2:1 of H1W because of precipitation at higher (2:1, 3:1 and 4:1) ratios. At physiological pH7.4 and a 1:1 metal-to-ligand molar ratio the tryptophan analogues of alloferon 1 form the CuH_-1L and/or CuH_-2L complexes with the 4N binding mode. The introduction of tryptophan in place of histidine residues changes the distribution diagram of the complexes formed with the change of pH and their stability constants compared to the respective substituted alanine analogues of alloferon 1. The CuH_-1L, CuH_-2L and CuH_-3L complexes of the tryptophan analogues are more stable from 1 to 5 log units in comparison to those of the alanine analogues. This stabilization of the complexes may result from cation(Cu(II))-π and indole/imidazole ring interactions. The induction of apoptosis in vivo, in Tenebrio molitor cells by the ligands and their copper(II) complexes at pH7.4 was studied. The biological results show that copper(II) ions in vivo did not cause any apparent apoptotic features. The most active were the H12W peptide and Cu(II)-H12W complex formed at pH7.4.