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

Abstract

In an attempt to investigate the role of histone H2B in Cu(II) induced toxicity and carcinogenesis, we synthesized the terminally blocked peptides H2B32–62 (SRKESYSVYVYKVLKQVH48PDTGISSKAMGIM) and Η2Β94–125 (IQTAVRLLLPGELAKH110AVSEGTKAVTKYTSS), mimicking the N-terminal histone-fold domain and C-terminal tail of histone H2B, respectively and studied their interaction with Cu(II) ions by means of potentiometric titrations and spectroscopic techniques (UV–visible, CD and EPR). Both peptides, H2B32–62 and H2B94–125, interacted efficiently with Cu(II) ions, forming several species from pH 4 to 11, with His48 and His110 serving as anchors for metal binding. In H2B32–62, the effective Cu(II) binding is emphasized by the formation of a soluble Cu(II)–H2B32–62 complex, unlike the unbound peptide that precipitated over pH 7.9. At physiological pH, both peptides form tetragonal 3N species with a {NIm, 2N−} coordination mode. At this pH, H2B32–62 presented the formation of coordination isomers, differentiated by the presence in one of them, of an axial coordination of the carboxylate group of Asp50. Copper binding with both H2B32–62 and H2B94–125 may induce a conformational change in the peptides' original structure. At physiological conditions, this effect may interfere with nucleosome's structure and dynamics, including the ubiquitination of Lys120 which is linked to gene silencing.