abstract
A linear decapeptide containing three His and one Asp residues and a β-turn-inducing dProPro unit was synthesised. A detailed potentiometric, mass spectrometric and spectroscopic study showed that at a 1:1 ratio of CCu /Cpeptide this peptide formed a major [CuH(OdPro Asp)](2+) species (pH range 5.5-7.0), in which the Cu(2+) ion was bound to the His and Asp residues in square-planar or square-pyramidal geometries. The stability constant corrected for protonated species (log K* CuH(O dPro-Asp)=9.33) is almost equal to the value obtained for the parent [CuH(OAsp)](2+) species (log K*CuH(O-Asp) =9.28), but lower than that obtained for the cyclic [CuH(CAsp)](2+) complex (log K*CuH(C-Asp) =10.79) previously published. Thus, the replacement of the ProGly unit by the stronger β-turn-inducing dProPro unit did not generate a more stable copper(II) species, although the OdPro Asp peptide was structured in solution, as shown by circular dichroism (CD) spectroscopy. Interestingly, the calculated value of Keff showed that this peptide behaved similarly to the OAsp or CAsp counterparts, depending on the pH value. The cyclic voltammetry data indicated that the most easily reducible species were [CuH(OAsp)](2+) (E'(0) =262 mV versus a normal hydrogen electrode (NHE)) and [CuH(OdPro Asp)](2+) (E'(0) =294 mV versus NHE) complexes, the peptidic scaffolds of which are open. A lower value was obtained for [CuH(CAsp)](2+) (E'(0) =24 mV versus NHE). A different degree of non-reversibility was observed for the three copper(II) complexes; this could reflect a different degree of flexibility in their respective peptidic scaffolds.
authors
Ana Fragoso, Tiago Carvalho, Pierre Rousselot-Pailley, Margarida M. Correia dos Santos, Rita Delgado, Olga Iranzo
our authors
