Design of a New Mimochrome with Unique Topology

Abstract

Peptide-based metalloprotein models represent useful systems to help understand how metalloproteins can support different functions, by the use of similar metal ion cofactors. In order to shed light on the role of the protein matrix in modulating the heme properties, we developed new models: mimochromes. They are pseudo-C(2) symmetric systems, composed of two helical peptides covalently linked to the deuteroporphyrin. The use of C(2) symmetry is particularly advantageous, because it simplifies the design, synthesis and characterization. However, it leaves the problem of possible diastereomeric forms. In the cobalt complex of the first derivative, mimochrome I, Lambda and Delta isomers were indeed experimentally observed. All the insights derived from the Co(III)-mimochrome I structure were used to obtain a re-designed molecule, mimochrome IV. The spectroscopic characterization of the iron and cobalt derivatives suggested the presence of the Lambda isomer as unique species. The NMR solution structure of the diamagnetic Co(III)-mimochrome IV confirmed the ability of the molecule to adopt a unique topology, and revealed the peptide chains to be in helical conformation, as designed. The insertion of intramolecular, inter-chain interactions was successful in favoring the formation of one of the two possible diastereomers. The stereochemically stable structure of mimochrome IV provides an attractive model for modulating the redox potential of the heme, by simple changing the peptide chain composition around the heme.

Protein Design: Toward Functional Metalloenzymes

“…928 It was demonstrated that Fe-mimochrome IV has a redox potential of −80 mV (vs NHE) at pH 7, which was also modulated by pH conditions. 268 This pH-dependence of redox potentials was attributed to the association of the His residues with the heme iron center, replacing an iron-bound axial water, and the deprotonation equilibrium of the other axial iron-bound water to an iron-bound hydroxide. Fe-mimochrome VI contains a 14-residue peptide with a His coordinating residue at the sixth position and a 10-residue peptide without an Fe-coordinating ligand, creating an asymmetric iron heme center.…”

Modulation of function in a minimalist heme-binding membrane protein

“…Water-soluble de novo designed heme proteins have long been used as models of more complicated, membraneembedded natural proteins that are involved in energy transduction [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Several factors, including heme solvent exposure [9,10], stabilization of the peptide scaffold [2,6,15], and local electrostatic interactions [7], have been shown to modulate the redox potential and proton coupling of the cofactor in these models.…”

The broad diversity of heme-protein cross-links: An overview

“…Using this reaction, Pavone and co-workers [113] developed a family of artificial models for heme proteins, namely mimochromes, by covalently linking a Fe(III)-deuterohemin to two Lys residues from separate peptide chains, with a histidine from each peptide chain coordinating axially to the heme iron. The Fe-mimochrome has a redox potential within the range observed for natural cytochromes, suggesting a plausible application in design of electrochemical biosensors [114]. Recently, Pavone and co-workers [115,116] designed a new artificial miniperoxidase (MP3) with a Fe(III)-deuterohemin covalently linked to a four-helix bundle, i.e., mimochromes VI (Fig.…”