A new metalloenzyme formed by a Fe(III)-mesoporphyrin IX functionalized by two helical decapeptides was synthesized to mimic function and structural features of a hemoprotein active site. Each decapeptide comprises six 2-aminoisobutyric acid residues, which constrain the peptide to attain a helical conformation, and three glutamic residues for improving the solubility of the catalyst in aqueous solutions. The new compound shows a marked amphiphilic character, featuring a polar outer surface and a hydrophobic inner cavity that hosts the reactants in a restrained environment where catalysis may occur. The catalytic activity of this synthetic mini-protein was tested with respect to the oxidation of L- and D-Dopa by hydrogen peroxide, showing moderate stereoselectivity. Structural information on the new catalyst and its adduct with the L- or D-Dopa substrate were obtained by the combined use of spectroscopic techniques and molecular mechanics calculations.
Keywords: Aib; Dopa oxidation kinetics; helical oligopeptides; hemoprotein models; mini-enzyme; peptide catalyst.
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