Interaction of Cu(ii) and Ni(ii) with the 63–93 fragment of histone H2B

Abstract

Chromatin proteins are believed to represent reactive sites for metal ion binding. We have synthesized the 31 amino acid peptide Ac-NSFVNDIFERIAGEASRLAHYNKRSTITSRE-NH2, corresponding to the 63-93 fragment of the histone H2B and studied its interaction with Cu(II) and Ni(II). Potentiometric and spectroscopic studies (UV-vis, CD, NMR and EPR) showed that histidine 21 acts as an anchoring binding site for the metal ion. Complexation of the studied peptide with Cu(II) starts at pH 4 with the formation of the monodentate species CuH2L. At physiological pH values, the 3N complex (N(Im), 2N(-)), CuL is favoured while at basic pH values the 4N (N(Im), 3N(-)) coordination mode is preferred. Ni(II) forms several complexes with the peptide starting from the distorted octahedral NiH2L at about neutral pH, to a square planar complex where the peptide is bound through a (N(Im), 3N(-)) mode in an equatorial plane at basic pH values. These results could be important in revealing more information about the mechanism of metal induced toxicity and carcinogenesis.

Copper effective binding with 32–62 and 94–125 peptide fragments of histone H2B

“…However, it can be characterized on the basis of its stoichiometry and stability constant. Indeed, the value log K* = −24.44 is typical for copper-peptide complexes with a {N Im , 3N − } coordination mode [35,46]. The value pK a = 8.72 which establishes the release of an additional proton from this complex is very close to the previously mentioned pK a value for the third amide deprotonation, explaining the low concentration of the CuLH − 3 species.…”

“…Our up to date reported results showed that both peptides form stable metal complexes, although H2B 63-93 presented a more effective binding towards Cu(II) than H2B 1-31 due to the absence of strong coordinating residues (such as, histidine or cysteine) in the latter [35,36]. These studies revealed an interesting increase in stability for the Cu(II)-H2B complexes compared to the species formed by -LAHYNK-peptide sharing the same binding sites, enhancing the importance of the side chains neighboring residues in the coordination process [33,35].…”

“…However, in our system, the saturation of the coordination sphere that has already occurred prevents the polynuclear complexes formation. On the other hand, the EPR parameters at pH 9.4 (Α || = 192 and g || = 2.204, Table 3) are typical for coordination of Cu(II) ion with a {N Im , 3N − amide } donor set [34,35,55], while the value λ max = 513 nm calculated by the absorption spectra is close with the one predicted from the equation of Sigel and Martin (λ max = 522 nm) [48], considering the presence of one imidazole and three amide nitrogen atoms in copper's coordination sphere. The latter also indicates that the binding of the Asp carboxyl group is no longer present.…”

“…The terminally blocked peptides, Ac-SRKESYSVYVYKVLKQVHPDT GISSKAMGIM-NH 2 (H2B 32-62 ) and Ac-IQTAVRLLLPGELAKHAVSEGT KAVTKYTSSK-NH 2 (H2B 94-125 ) were synthesized on a Sieber amide resin using Fmoc/tBu chemistry on the standard method of solid phase peptide synthesis, as previously described [35]. Peptides' purity (over 98%) and identity was confirmed by means of electrospray ionisation-mass spectrometry ( …”

“…These studies revealed an interesting increase in stability for the Cu(II)-H2B complexes compared to the species formed by -LAHYNK-peptide sharing the same binding sites, enhancing the importance of the side chains neighboring residues in the coordination process [33,35].…”