<p>In panel A the arrows indicate the more likely Hg<sup>2+</sup> ligands. Imid... more <p>In panel A the arrows indicate the more likely Hg<sup>2+</sup> ligands. Imidazole groups are arbitrarily shown with the proton at the Nε atom. The dashed line highlights the group shown in details in panel B.</p
<p>Fluorescence emission spectra recorded after excitation at 340 nm, of dH3w (7 μM) in the... more <p>Fluorescence emission spectra recorded after excitation at 340 nm, of dH3w (7 μM) in the absence (black lines) and in the presence of increasing concentrations of Hg<sup>2+</sup>, at pH 8.0 (A), 6.0 (B) and 4.0 (C).</p
<p>Fluorescence emission spectra of dH3w (7 μM) in the absence (black line) and in the pres... more <p>Fluorescence emission spectra of dH3w (7 μM) in the absence (black line) and in the presence of increasing concentrations of Hg<sup>2+</sup> (1, 3, 5, 10, 12, 15, 20, 30, 50, 100 μM) at pH 7.0.</p
The miniaturized metalloenzyme Fe(III)-mimochrome VI*a (Fe(III)-MC6*a) acts as an excellent bioca... more The miniaturized metalloenzyme Fe(III)-mimochrome VI*a (Fe(III)-MC6*a) acts as an excellent biocatalyst in the H 2 O 2-mediated oxidative dehalogenation of the well-known pesticide and biocide 2,4,6trichlorophenol (TCP). The artificial enzyme can oxidize TCP with a catalytic efficiency (k cat /K TCP m ¼ 150 000 mM À1 s À1) up to 1500-fold higher than the most active natural metalloenzyme horseradish peroxidase (HRP). UV-visible and EPR spectroscopies were used to provide indications of the catalytic mechanism. One equivalent of H 2 O 2 fully converts Fe(III)-MC6*a into the oxoferryl-porphyrin radical cation intermediate [(Fe(IV)]O)porc + ], similarly to peroxidase compound I (Cpd I). Addition of TCP to Cpd I rapidly leads to the formation of the corresponding quinone, while Cpd I decays back to the ferric resting state in the absence of substrate. EPR data suggest a catalytic mechanism involving two consecutive one-electron reactions. All results highlight the value of the miniaturization strategy for the development of chemically stable, highly efficient artificial metalloenzymes as powerful catalysts for the oxidative degradation of toxic pollutants.
<p>The dashed lines highlighted the found binding stoichiometry at mole fraction of dH3w of... more <p>The dashed lines highlighted the found binding stoichiometry at mole fraction of dH3w of 0.52 and 0.34 which correspond to 1:1 and 1:2 (dH3w:Hg<sup>2+</sup>) complexes, respectively. The experiment was carried out in 20 mM Mops buffer, pH 7.0 at the temperature of 25 °C. Errors are not shown because they were always smaller than the symbols sizes.</p
De novo design has proven a powerful methodology for understanding protein folding and function, ... more De novo design has proven a powerful methodology for understanding protein folding and function, and for mimicking or even bettering the properties of natural proteins. Extensive progress has been made in the design of helical bundles, simple structural motifs that can be nowadays designed with a high degree of precision. Among helical bundles, the four-helix bundle is widespread in nature, and is involved in numerous and fundamental processes. Representative examples are the carboxylate bridged diiron proteins, which perform a variety of different functions, ranging from reversible dioxygen binding to catalysis of dioxygen-dependent reactions, including epoxidation, desaturation, monohydroxylation, and radical formation. The "Due Ferri" (two-irons; DF) family of proteins is the result of a de novo design approach, aimed to reproduce in minimal four-helix bundle models the properties of the more complex natural diiron proteins, and to address how the amino acid sequence modulates their functions. The results so far obtained point out that asymmetric metal environments are essential to reprogram functions, and to achieve the specificity and selectivity of the natural enzymes. Here, we describe a design method that allows constructing asymmetric four-helix bundles through the covalent heterodimerization of two different α-helical harpins. In particular, starting from the homodimeric DF3 structure, we developed a protocol for covalently linking the two α2 monomers by using the Cu(I) catalyzed azide-alkyne cycloaddition. The protocol was then generalized, in order to include the construction of several linkers, in different protein positions. Our method is fast, low cost, and in principle can be applied to any couple of peptides/proteins we desire to link.
JBIC Journal of Biological Inorganic Chemistry, 2010
The design, synthesis, and metal-binding properties of DF3, a new de novo designed di-iron protei... more The design, synthesis, and metal-binding properties of DF3, a new de novo designed di-iron protein model are described ("DF" represents due ferri, Italian for "two iron," "di-iron"). DF3 is the latest member of the DF family of synthetic proteins. They consist of helix-loop-helix hairpins, designed to dimerize and form an antiparallel four-helix bundle that encompasses a metal-binding site similar to those of non-heme carboxylate-bridged di-iron proteins. Unlike previous DF proteins, DF3 is highly soluble in water (up to 3 mM) and forms stable complexes with several metal ions (Zn, Co, and Mn), with the desired secondary structure and the expected stoichiometry of two ions per protein. UV-vis studies of Co(II) and Fe(III) complexes confirm a metal-binding environment similar to previous di-Co(II)-and di-Fe(III)-DF proteins, including the presence of a µ-oxo-di-Fe(III) unit. Interestingly, UV-vis, EPR, and resonance Raman studies
Bioinorganic chemists tackled the challenge to unravel the mechanisms that allow the protein matr... more Bioinorganic chemists tackled the challenge to unravel the mechanisms that allow the protein matrix to modulate the catalytic activity of metal-containing cofactors through the development of artificial systems. In this perspective, heme-proteins represent a significant source of inspiration: researchers have attempted for decades to develop efficient and selective metalloporphyrin-based catalysts. Significant advance has been achieved in the design and engineering of protein scaffolds to host metalloporphyrins and to modulate their reactivity. Peptidebased architectures of different sizes have been exploited for the construction of catalytic systems. Among them, synthetic porphyrin-peptide conjugates known as "Mimochromes" represent an important class of artificial heme enzymes. Their structure consists of two α-helical peptides covalently linked to a metalloporphyrin core, resulting into a helix-heme-helix sandwich. Their simple scaffold has been optimized to reproduce the functional properties of peroxidases. Mimochrome VI*a (MC6*a), in its Fe III complex, recently emerged as the best artificial peroxidase known so far, overcoming the catalytic efficiency of horseradish peroxidase (HRP) in ABTS oxidation. Moreover, the cobalt derivative (Co-MC6*a) behaves as a very promising catalyst in hydrogen evolution reactions. These recent achievements prompted us to further evaluate the versatility of the MC6*a scaffold towards metal replacement, by swapping iron to manganese. The primary aim of this PhD project was to expand the scope of transformations accessible by MC6*a complexes in oxidation chemistry. Taking into account the catalytic promiscuity of iron and manganese porphyrins towards diverse oxidative transformations, the analysis of the spectroscopic, redox and catalytic properties of Fe-and Mn-MC6*a has been performed. 2 Compared to other peptide-porphyrin conjugates with a fully solvent-exposed distal site, both Fe-and Mn-MC6*a display an increased ability to promote the deprotonation of metal-bound water and hydrogen peroxide. This property allows MC6*a complexes to reach their highest activity towards H2O2 at lower pH values, approaching those of the natural counterparts. Both Fe-and Mn-MC6*a demonstrated to be efficient and robust catalysts in the H2O2-mediated sulfoxidation of thioethers, being among the most active artificial heme enzymes studied for this reaction. The two catalysts displayed divergent behaviours towards the oxidation of indole. Notably, Mn-MC6*a displays higher chemo-selectivity compared to Fe-MC6*a, but also surpasses most of hemeenzymes examined to the same end. Mn-MC6*a represents one of the most proficient catalysts for indole oxidation, mainly due to the possibility of controlling the formation of different oxidation products with high selectivity. Among them, the formation and isolation of the highly reactive 3-oxindolenine is very important, because it could represent a useful synthon in organic synthesis. Overall, the results of this PhD thesis pave the way for the application of mimochromes to synthetic chemistry. These catalysts fill the middle ground between small-molecule and biological catalysts, since they own a minimal structure that enables substrate promiscuity and a designed peptide scaffold that modulates the reactivity of the metal ion.
Understanding the structural determinants for metal ion coordination in metalloproteins is a fund... more Understanding the structural determinants for metal ion coordination in metalloproteins is a fundamental issue for designing metal binding sites with predetermined geometry and activity. In order to achieve this, we report in this paper the design, synthesis and metal binding properties of METP3, a homodimer made up of a small peptide, which self assembles in the presence of tetrahedrally coordinating metal ions. METP3 was obtained through a redesign approach, starting from the previously developed METP molecule. The undecapeptide sequence of METP, which dimerizes to house a Cys4 tetrahedral binding site, was redesigned in order to accommodate a Cys2His2 site. The binding properties of METP3 were determined toward different metal ions. Successful assembly of METP3 with Co(II), Zn(II) and Cd(II), in the expected 2:1 stoichiometry and tetrahedral geometry was proven by UV-visible spectroscopy. CD measurements on both the free and metal-bound forms revealed that the metal coordination ...
Indole oxidation represents a real challenge for selectivity because it typically leads to comple... more Indole oxidation represents a real challenge for selectivity because it typically leads to complex mixtures of products even when highly selective enzymes are used. Here, we describe the catalytic potential of an artificial enzyme, Mn-Mimochrome VI*a (Mn-MC6*a), in promoting indole oxidation. This mini-enzyme contains a manganese−deuteroporphyrin active site within a scaffold of two synthetic small peptides covalently linked to porphyrin. Mn-MC6*a promotes the selective oxidation of indole at its C3 position, leading to a 3-oxindole derivative (2-TFE-3oxindole) with unprecedented product selectivity (86% at pH 8.5) compared to native or artificial heme-enzymes. We also suggest a possible reaction mechanism based on the effect of pH, cosolvent, and indole substitution on the reaction outcome. These studies demonstrate that Mn-MC6*a is an excellent artificial peroxygenase for the production of 3-oxindole-containing compounds as key building blocks for the synthesis of fine chemicals.
Heavy metals are hazardous environmental contaminants, often highly toxic even at extremely low c... more Heavy metals are hazardous environmental contaminants, often highly toxic even at extremely low concentrations. Monitoring their presence in environmental samples is an important but complex task that has attracted the attention of many research groups. We have previously developed a fluorescent peptidyl sensor, dH3w, for monitoring Zn 2+ in living cells. This probe, designed on the base on the internal repeats of the human histidine rich glycoprotein, shows a turn on response to Zn 2+ and a turn off response to Cu 2+. Other heavy metals (Mn 2+ , Fe 2+ , Ni 2+ , Co 2+ , Pb 2+ and Cd 2+) do not interfere with the detection of Zn 2+ and Cu 2+. Here we report that dH3w has an affinity for Hg 2+ considerably higher than that for Zn 2+ or Cu 2+ , therefore the strong fluorescence of the Zn 2+ /dH3w complex is quenched when it is exposed to aqueous solutions of Hg 2+ , allowing the detection of sub-micromolar levels of Hg 2+. Fluorescence of the Zn 2+ /dH3w complex is also quenched by Cu 2+ whereas other heavy metals (Mn 2+ , Fe 2+ , Ni 2+ , Co 2+ , Cd 2+ , Pb 2+ , Sn 2+ and Cr 3+) have no effect. The high affinity and selectivity suggest that dH3w and the Zn 2+ /dH3w complex are suited as fluorescent sensor for the detection of Hg 2+ and Cu 2+ in environmental as well as biological samples.
Manganese-porphyrins are important tools in catalysis, due to their capability to promote a wide ... more Manganese-porphyrins are important tools in catalysis, due to their capability to promote a wide variety of synthetically valuable transformations. Despite their great reactivity, the difficulties to control the reaction selectivity and to protect the catalyst from self-degradation hamper their practical application. Compared to small-molecule porphyrin complexes, metalloenzymes display remarkable features, because the reactivity of the metal center is finely modulated by a complex interplay of interactions within the protein matrix. In the effort to combine the catalytic potential of manganese porphyrins with the unique properties of biological catalysts, artificial metalloenzymes have been reported, mainly by incorporation of manganese-porphyrins into native protein scaffolds. Here we describe the spectroscopic and catalytic properties of Mn-Mimochrome VI * a (Mn-MC6 * a), a mini-protein with a manganese deuteroporphyrin active site within a scaffold of two synthetic peptides covalently bound to the porphyrin. Mn-MC6 * a is an efficient catalyst endowed with peroxygenase activity. The UV-vis absorption spectrum of Mn-MC6 * a resembles that of Mn-reconstituted horseradish peroxidase (Mn-HRP), both in the resting and high-valent oxidized states. Remarkably, Mn-MC6 * a shows a higher reactivity compared to Mn-HRP, because higher yields and chemoselectivity were observed in thioether oxidation. Experimental evidences also provided indications on the nature of the high-valent reactive intermediate and on the sulfoxidation mechanism.
<p>In panel A the arrows indicate the more likely Hg<sup>2+</sup> ligands. Imid... more <p>In panel A the arrows indicate the more likely Hg<sup>2+</sup> ligands. Imidazole groups are arbitrarily shown with the proton at the Nε atom. The dashed line highlights the group shown in details in panel B.</p
<p>Fluorescence emission spectra recorded after excitation at 340 nm, of dH3w (7 μM) in the... more <p>Fluorescence emission spectra recorded after excitation at 340 nm, of dH3w (7 μM) in the absence (black lines) and in the presence of increasing concentrations of Hg<sup>2+</sup>, at pH 8.0 (A), 6.0 (B) and 4.0 (C).</p
<p>Fluorescence emission spectra of dH3w (7 μM) in the absence (black line) and in the pres... more <p>Fluorescence emission spectra of dH3w (7 μM) in the absence (black line) and in the presence of increasing concentrations of Hg<sup>2+</sup> (1, 3, 5, 10, 12, 15, 20, 30, 50, 100 μM) at pH 7.0.</p
The miniaturized metalloenzyme Fe(III)-mimochrome VI*a (Fe(III)-MC6*a) acts as an excellent bioca... more The miniaturized metalloenzyme Fe(III)-mimochrome VI*a (Fe(III)-MC6*a) acts as an excellent biocatalyst in the H 2 O 2-mediated oxidative dehalogenation of the well-known pesticide and biocide 2,4,6trichlorophenol (TCP). The artificial enzyme can oxidize TCP with a catalytic efficiency (k cat /K TCP m ¼ 150 000 mM À1 s À1) up to 1500-fold higher than the most active natural metalloenzyme horseradish peroxidase (HRP). UV-visible and EPR spectroscopies were used to provide indications of the catalytic mechanism. One equivalent of H 2 O 2 fully converts Fe(III)-MC6*a into the oxoferryl-porphyrin radical cation intermediate [(Fe(IV)]O)porc + ], similarly to peroxidase compound I (Cpd I). Addition of TCP to Cpd I rapidly leads to the formation of the corresponding quinone, while Cpd I decays back to the ferric resting state in the absence of substrate. EPR data suggest a catalytic mechanism involving two consecutive one-electron reactions. All results highlight the value of the miniaturization strategy for the development of chemically stable, highly efficient artificial metalloenzymes as powerful catalysts for the oxidative degradation of toxic pollutants.
<p>The dashed lines highlighted the found binding stoichiometry at mole fraction of dH3w of... more <p>The dashed lines highlighted the found binding stoichiometry at mole fraction of dH3w of 0.52 and 0.34 which correspond to 1:1 and 1:2 (dH3w:Hg<sup>2+</sup>) complexes, respectively. The experiment was carried out in 20 mM Mops buffer, pH 7.0 at the temperature of 25 °C. Errors are not shown because they were always smaller than the symbols sizes.</p
De novo design has proven a powerful methodology for understanding protein folding and function, ... more De novo design has proven a powerful methodology for understanding protein folding and function, and for mimicking or even bettering the properties of natural proteins. Extensive progress has been made in the design of helical bundles, simple structural motifs that can be nowadays designed with a high degree of precision. Among helical bundles, the four-helix bundle is widespread in nature, and is involved in numerous and fundamental processes. Representative examples are the carboxylate bridged diiron proteins, which perform a variety of different functions, ranging from reversible dioxygen binding to catalysis of dioxygen-dependent reactions, including epoxidation, desaturation, monohydroxylation, and radical formation. The "Due Ferri" (two-irons; DF) family of proteins is the result of a de novo design approach, aimed to reproduce in minimal four-helix bundle models the properties of the more complex natural diiron proteins, and to address how the amino acid sequence modulates their functions. The results so far obtained point out that asymmetric metal environments are essential to reprogram functions, and to achieve the specificity and selectivity of the natural enzymes. Here, we describe a design method that allows constructing asymmetric four-helix bundles through the covalent heterodimerization of two different α-helical harpins. In particular, starting from the homodimeric DF3 structure, we developed a protocol for covalently linking the two α2 monomers by using the Cu(I) catalyzed azide-alkyne cycloaddition. The protocol was then generalized, in order to include the construction of several linkers, in different protein positions. Our method is fast, low cost, and in principle can be applied to any couple of peptides/proteins we desire to link.
JBIC Journal of Biological Inorganic Chemistry, 2010
The design, synthesis, and metal-binding properties of DF3, a new de novo designed di-iron protei... more The design, synthesis, and metal-binding properties of DF3, a new de novo designed di-iron protein model are described ("DF" represents due ferri, Italian for "two iron," "di-iron"). DF3 is the latest member of the DF family of synthetic proteins. They consist of helix-loop-helix hairpins, designed to dimerize and form an antiparallel four-helix bundle that encompasses a metal-binding site similar to those of non-heme carboxylate-bridged di-iron proteins. Unlike previous DF proteins, DF3 is highly soluble in water (up to 3 mM) and forms stable complexes with several metal ions (Zn, Co, and Mn), with the desired secondary structure and the expected stoichiometry of two ions per protein. UV-vis studies of Co(II) and Fe(III) complexes confirm a metal-binding environment similar to previous di-Co(II)-and di-Fe(III)-DF proteins, including the presence of a µ-oxo-di-Fe(III) unit. Interestingly, UV-vis, EPR, and resonance Raman studies
Bioinorganic chemists tackled the challenge to unravel the mechanisms that allow the protein matr... more Bioinorganic chemists tackled the challenge to unravel the mechanisms that allow the protein matrix to modulate the catalytic activity of metal-containing cofactors through the development of artificial systems. In this perspective, heme-proteins represent a significant source of inspiration: researchers have attempted for decades to develop efficient and selective metalloporphyrin-based catalysts. Significant advance has been achieved in the design and engineering of protein scaffolds to host metalloporphyrins and to modulate their reactivity. Peptidebased architectures of different sizes have been exploited for the construction of catalytic systems. Among them, synthetic porphyrin-peptide conjugates known as "Mimochromes" represent an important class of artificial heme enzymes. Their structure consists of two α-helical peptides covalently linked to a metalloporphyrin core, resulting into a helix-heme-helix sandwich. Their simple scaffold has been optimized to reproduce the functional properties of peroxidases. Mimochrome VI*a (MC6*a), in its Fe III complex, recently emerged as the best artificial peroxidase known so far, overcoming the catalytic efficiency of horseradish peroxidase (HRP) in ABTS oxidation. Moreover, the cobalt derivative (Co-MC6*a) behaves as a very promising catalyst in hydrogen evolution reactions. These recent achievements prompted us to further evaluate the versatility of the MC6*a scaffold towards metal replacement, by swapping iron to manganese. The primary aim of this PhD project was to expand the scope of transformations accessible by MC6*a complexes in oxidation chemistry. Taking into account the catalytic promiscuity of iron and manganese porphyrins towards diverse oxidative transformations, the analysis of the spectroscopic, redox and catalytic properties of Fe-and Mn-MC6*a has been performed. 2 Compared to other peptide-porphyrin conjugates with a fully solvent-exposed distal site, both Fe-and Mn-MC6*a display an increased ability to promote the deprotonation of metal-bound water and hydrogen peroxide. This property allows MC6*a complexes to reach their highest activity towards H2O2 at lower pH values, approaching those of the natural counterparts. Both Fe-and Mn-MC6*a demonstrated to be efficient and robust catalysts in the H2O2-mediated sulfoxidation of thioethers, being among the most active artificial heme enzymes studied for this reaction. The two catalysts displayed divergent behaviours towards the oxidation of indole. Notably, Mn-MC6*a displays higher chemo-selectivity compared to Fe-MC6*a, but also surpasses most of hemeenzymes examined to the same end. Mn-MC6*a represents one of the most proficient catalysts for indole oxidation, mainly due to the possibility of controlling the formation of different oxidation products with high selectivity. Among them, the formation and isolation of the highly reactive 3-oxindolenine is very important, because it could represent a useful synthon in organic synthesis. Overall, the results of this PhD thesis pave the way for the application of mimochromes to synthetic chemistry. These catalysts fill the middle ground between small-molecule and biological catalysts, since they own a minimal structure that enables substrate promiscuity and a designed peptide scaffold that modulates the reactivity of the metal ion.
Understanding the structural determinants for metal ion coordination in metalloproteins is a fund... more Understanding the structural determinants for metal ion coordination in metalloproteins is a fundamental issue for designing metal binding sites with predetermined geometry and activity. In order to achieve this, we report in this paper the design, synthesis and metal binding properties of METP3, a homodimer made up of a small peptide, which self assembles in the presence of tetrahedrally coordinating metal ions. METP3 was obtained through a redesign approach, starting from the previously developed METP molecule. The undecapeptide sequence of METP, which dimerizes to house a Cys4 tetrahedral binding site, was redesigned in order to accommodate a Cys2His2 site. The binding properties of METP3 were determined toward different metal ions. Successful assembly of METP3 with Co(II), Zn(II) and Cd(II), in the expected 2:1 stoichiometry and tetrahedral geometry was proven by UV-visible spectroscopy. CD measurements on both the free and metal-bound forms revealed that the metal coordination ...
Indole oxidation represents a real challenge for selectivity because it typically leads to comple... more Indole oxidation represents a real challenge for selectivity because it typically leads to complex mixtures of products even when highly selective enzymes are used. Here, we describe the catalytic potential of an artificial enzyme, Mn-Mimochrome VI*a (Mn-MC6*a), in promoting indole oxidation. This mini-enzyme contains a manganese−deuteroporphyrin active site within a scaffold of two synthetic small peptides covalently linked to porphyrin. Mn-MC6*a promotes the selective oxidation of indole at its C3 position, leading to a 3-oxindole derivative (2-TFE-3oxindole) with unprecedented product selectivity (86% at pH 8.5) compared to native or artificial heme-enzymes. We also suggest a possible reaction mechanism based on the effect of pH, cosolvent, and indole substitution on the reaction outcome. These studies demonstrate that Mn-MC6*a is an excellent artificial peroxygenase for the production of 3-oxindole-containing compounds as key building blocks for the synthesis of fine chemicals.
Heavy metals are hazardous environmental contaminants, often highly toxic even at extremely low c... more Heavy metals are hazardous environmental contaminants, often highly toxic even at extremely low concentrations. Monitoring their presence in environmental samples is an important but complex task that has attracted the attention of many research groups. We have previously developed a fluorescent peptidyl sensor, dH3w, for monitoring Zn 2+ in living cells. This probe, designed on the base on the internal repeats of the human histidine rich glycoprotein, shows a turn on response to Zn 2+ and a turn off response to Cu 2+. Other heavy metals (Mn 2+ , Fe 2+ , Ni 2+ , Co 2+ , Pb 2+ and Cd 2+) do not interfere with the detection of Zn 2+ and Cu 2+. Here we report that dH3w has an affinity for Hg 2+ considerably higher than that for Zn 2+ or Cu 2+ , therefore the strong fluorescence of the Zn 2+ /dH3w complex is quenched when it is exposed to aqueous solutions of Hg 2+ , allowing the detection of sub-micromolar levels of Hg 2+. Fluorescence of the Zn 2+ /dH3w complex is also quenched by Cu 2+ whereas other heavy metals (Mn 2+ , Fe 2+ , Ni 2+ , Co 2+ , Cd 2+ , Pb 2+ , Sn 2+ and Cr 3+) have no effect. The high affinity and selectivity suggest that dH3w and the Zn 2+ /dH3w complex are suited as fluorescent sensor for the detection of Hg 2+ and Cu 2+ in environmental as well as biological samples.
Manganese-porphyrins are important tools in catalysis, due to their capability to promote a wide ... more Manganese-porphyrins are important tools in catalysis, due to their capability to promote a wide variety of synthetically valuable transformations. Despite their great reactivity, the difficulties to control the reaction selectivity and to protect the catalyst from self-degradation hamper their practical application. Compared to small-molecule porphyrin complexes, metalloenzymes display remarkable features, because the reactivity of the metal center is finely modulated by a complex interplay of interactions within the protein matrix. In the effort to combine the catalytic potential of manganese porphyrins with the unique properties of biological catalysts, artificial metalloenzymes have been reported, mainly by incorporation of manganese-porphyrins into native protein scaffolds. Here we describe the spectroscopic and catalytic properties of Mn-Mimochrome VI * a (Mn-MC6 * a), a mini-protein with a manganese deuteroporphyrin active site within a scaffold of two synthetic peptides covalently bound to the porphyrin. Mn-MC6 * a is an efficient catalyst endowed with peroxygenase activity. The UV-vis absorption spectrum of Mn-MC6 * a resembles that of Mn-reconstituted horseradish peroxidase (Mn-HRP), both in the resting and high-valent oxidized states. Remarkably, Mn-MC6 * a shows a higher reactivity compared to Mn-HRP, because higher yields and chemoselectivity were observed in thioether oxidation. Experimental evidences also provided indications on the nature of the high-valent reactive intermediate and on the sulfoxidation mechanism.
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Papers by Linda Leone