Design and Semisynthesis of Photoactive Myoglobin Bearing Ruthenium Tris(2,2'-bipyridine) Using Cofactor-Reconstitution

Profiling the Heme-Binding Proteomes of Bacteria Using Chemical Proteomics

Heme is a cofactor with myriad roles and essential to almost all living organisms. Beyond classical gas transport and catalytic functions, heme is increasingly appreciated as a tightly controlled signalling molecule regulating protein expression. However, heme acquisition, biosynthesis and regulation is poorly understood beyond a few model organisms, and the heme-binding proteome has not been fully characterised in bacteria. Yet as heme homeostasis is critical for bacterial survival, heme-binding proteins are promising drug targets. Herein we report a chemical proteomics method for global profiling of heme-binding proteins in live cells for the first time. Employing a panel of heme-based clickable and photoaffinity probes enabled the profiling of 32-54 % of the known heme-binding proteomes in Gram-positive and Gram-negative bacteria. This simple-to-implement profiling strategy could be interchangeably applied to different cell types and systems and fuel future research into heme biology.

The Red Color of Life Transformed - Synthetic Advances and Emerging Applications of Protoporphyrin IX in Chemical Biology

Protoporphyrin IX (PPIX) is the porphyrin scaffold of heme b, a ubiquitous prosthetic group of proteins responsible for oxygen binding (hemoglobin, myoglobin), electron transfer (cytochrome c) and catalysis (cytochrome P450, catalases, peroxidases). PPIX and its metallated derivatives frequently find application as therapeutic agents, imaging tools, catalysts, sensors and in light harvesting. The vast toolkit of accessible porphyrin functionalization reactions enables easy synthetic modification of PPIX to meet the requirements for its multiple uses. In the past few years, particular interest has arisen in exploiting the interaction of PPIX and its synthetic derivatives with biomolecules such as DNA and heme-binding proteins to evolve molecular devices with new functions as well as to uncover potential therapeutic toeholds. This review strives to shine a light on the most recent developments in the synthetic chemistry of PPIX and its uses in selected fields of chemical biology.

Photochemical and photophysical behaviour of porphyrins and phthalocyanines irradiated with violet or ultraviolet light

Photochemical irradiation of porphyrins or phthalocyanines with violet or ultraviolet light absorbed by their second or higher absorption bands populates their higher excited states. These higher excited states generally dissipate very rapidly, but, competing with such rapid deactivation, often show unique behaviour different from the lowest excited states populated under visible light irradiation of the first absorption band, namely wavelength-dependent reactions or emission. The higher excited states often exhibit characteristic emission and enhanced reactivity in electron transfer, energy transfer and so on, competing with rapid deactivation. This paper attempts to summarize our work, perfomed particularly by means of femtosecond spectroscopy, and recent progress in this area.

Photophysical and DNA-binding properties of cytochrome c modified with a platinum(II) complex

Cytochrome c (cyt c) derivatives modified with a platinum(II) complex at the lysine residue, cyt c(III)-[Pt(bpy)(dapap)](1) {bpy = 2,2'-bipyridine, and dapap = 3-(2,3-diaminopropionylamino)propionic acid}, have been prepared. The modified residues are Lys8, Lys13, Lys55, Lys60, Lys73, and Lys88. In the case of the cyt c(III)-[Pt(bpy)(dapap)](1) dyad, the photoexcited singlet state of (1)([Pt(bpy)(dapap)](1))* was quenched by the heme Fe(III) moiety through the intramolecular photoinduced energy-transfer reaction via a through-space mechanism. Next, in the presence of calf thymus (CT)-DNA, the DNA-responsive fluorescence properties of cyt c(III)-[Pt(bpy)(dapap)](1) isomers were investigated. The order of the obtained binding constants between the cyt c(III)-[Pt(bpy)(dapap)](1) isomer and CT-DNA in an aqueous solution suggested that the electrostatic interaction is one of the important factors to stabilize the cyt c-DNA complex. Finally, we discussed the rotational motion of the [Pt(bpy)(dapap)](2+) moiety at the surface of cyt c by fluorescence anisotropy measurement. The increase in the anisotropy parameter, r, for each cyt c isomer clearly revealed that the noncovalent recognition of the [Pt(bpy)(dapap)](2+) moiety by CT-DNA is an essential event in the formation of the cyt c-DNA complex and generation of DNA-sensitive fluorescence signals.

Addressable DNA-myoglobin photocatalysis

Photoactivatable myoglobin containing a DNA oligonucleotide as a structural anchor was designed by using the reconstitution of artificial heme moieties containing Ru(3+) ions. This semisynthetic DNA-enzyme conjugate was successfully used for the oxidation of peroxidase substrates by using visible light instead of H(2)O(2) for the activation. The DNA anchor was utilized for the immobilization of the enzyme on the surface of magnetic microbeads. Enzyme activity measurements not only indicated undisturbed biofunctionality of the tethered DNA but also enabled magnetic separation-based enrichment and recycling of the photoactivatable biocatalyst.

Apoenzyme reconstitution as a chemical tool for structural enzymology and biotechnology

Many enzymes contain a nondiffusible organic cofactor, often termed a prosthetic group, which is located in the active site and essential for the catalytic activity of the enzyme. These cofactors can often be extracted from the protein to yield the respective apoenzyme, which can subsequently be reconstituted with an artificial analogue of the native cofactor. Nowadays a large variety of synthetic cofactors can be used for the reconstitution of apoenzymes and, thus, generate novel semisynthetic enzymes. This approach has been refined over the past decades to become a versatile tool of structural enzymology to elucidate structure-function relationships of enzymes. Moreover, the reconstitution of apoenzymes can also be used to generate enzymes possessing enhanced or even entirely new functionality. This Review gives an overview on historical developments and the current state-of-the-art on apoenzyme reconstitution.

Metal ion-dependent fluorescent dynamics of photoexcited zinc-porphyrin and zinc-myoglobin modified with ethylenediaminetetraacetic acid

The reconstituted zinc-myoglobin (ZnMb) dyads, ZnMb-[M(II)(edta)], have been prepared by incorporating a zinc-porphyrin (ZnP) cofactor modified with ethylenediaminetetraacetic acid (H(4)edta) into apo-Mb. In case of the monomeric ZnP(edta) cofactor coordinated by one pyridine molecule, ZnP(py)(edta), a spontaneous 1:1 complex with a transient metal ion was formed in an aqueous solvent, and the photoexcited singlet state of ZnP, (1)(ZnP)*, was quenched by the [Cu(II)(edta)] moiety through intramolecular photoinduced electron-transfer (ET) reaction. The rate constant for the intramolecular quenching ET (k(q)) at 25 degrees C was successfully obtained as k(q) = 5.1 x 10(9) s(-1). In the case of Co(2+), Ni(2+), and Mn(2+), intersystem crossing by paramagnetic effect was mainly considered between (1)(ZnP)* and the [M(II)(edta)] complex. For the ZnMb-[M(II)(edta)] systems, the intramolecular ET reaction between the excited singlet state of (1)(ZnMb)* and the [Cu(II)(edta)] moieties provided the slower quenching rate constant, k(q) = 2.1 x 10(8) s(-1), compared with that of the ZnP(py)(edta) one. Kinetic studies also presented the efficient fluorescence quenching of the (1)(ZnMb)*-[Co(II)(edta)] dyad. Our study clearly demonstrates that wrapping of the ZnP cofactor by the apoprotein matrix and synthetic manipulation at the Mb surface ensure metal ion-sensitive fluorescent dynamics of ZnMb and provides valuable information to elucidate the complicated mechanism of the biological photoinduced ET reactions of hemoproteins.

Electronic and fluorescence spectral studies of a novel porphyrin-polypyridyl ruthenium(II) hybrid linked by a butyl chain

The electronic and fluorescence spectroscopic properties of a novel porphyrin-polypyridyl ruthenium(II) hybrid, [C(4)-TPP-(ip)Ru(phen)(2)](ClO(4))(2) (TPP=5,10,15,20-tetraphenylporphyrin, ip=imidazo[4,5-f][1,10]phenanthroline and phen=1,10-Phenanthroline), in which a polypyridyl ruthenium(II) moiety is linked to a porphyrin moiety by a butyl chain have been investigated and compared to its corresponding reference compounds. The studies of electronic absorption spectra have shown that there is an electronic interaction between the porphyrin moiety and the polypyridyl ruthenium(II) moiety in the hybrid. It can be found that intramolecular photoinduced electron and energy transfer processes may occur in the hybrid from the fluorescence spectra. When exciting in Soret band and Q band of porphyrin, the fluorescence quenching of the porphyrin moiety of the hybrid takes place due to electron transfer from the lowest singlet excited state (S(1)) to the appended polypyridyl rutherium(II) moiety, while the decay of S(2) (the second-excited singlet state) of the porphyrin moiety is mainly contributed to internal conversion to S(1). When exciting in MLCT band of the polypyridyl ruthenium(II) moiety, fluorescence corresponding to the polypyridyl ruthenium(II) moiety is quenched by intramolecular energy transfer from (3)MLCT of the ruthenium moiety to the lowest-energy triplet state localized on the porphyrin moiety.

Aggregation Behavior of Giant Amphiphiles Prepared by Cofactor Reconstitution

We report on biohybrid surfactants, termed "giant amphiphiles", in which a protein or an enzyme acts as the polar head group and a synthetic polymer as the apolar tail. It is demonstrated that the modification of horseradish peroxidase (HRP) and myoglobin (Mb) with an apolar polymer chain through the cofactor reconstitution method yields giant amphiphiles that form spherical aggregates (vesicles) in aqueous solution. Both HRP and Mb retain their original functionality when modified with a single polystyrene chain, but reconstitution has an effect on their activities. In the case of HRP the enzymatic activity decreases and for Mb the stability of the dioxygen myoglobin (oxy-Mb) complex is reduced, which is probably the result of a disturbed binding of the heme in the apo-protein or a reduced access of the substrate to the active site of the enzyme or protein.

A four-electron O(2)-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V

O2 was electroreduced to water, at a true-surface-area-based current density of 0.5 mA cm-2, at 37 degrees C and at pH 5 on a "wired" laccase bioelectrocatalyst-coated carbon fiber cathode. The polarization (potential vs the reversible potential of the O2 /H2O half-cell in the same electrolyte) of the cathode was only -0.07 V, approximately one-fifth of the -0.37 V polarization of a smooth platinum fiber cathode, operating in its optimal electrolyte, 0.5 M H2SO4. The bioelectrocatalyst was formed by "wiring" laccase to carbon through an electron conducting redox hydrogel, its redox functions tethered through long and flexible spacers to its cross-linked and hydrated polymer. Incorporation of the tethers increased the apparent electron diffusion coefficient 100-fold to (7.6 +/- 0.3) x 10-7 cm 2 s-1. A miniature single-compartment glucose-O2 biofuel cell made with the novel cathode operated optimally at 0.88 V, the highest operating voltage for a compartmentless miniature fuel cell.

Highly Coupled Dyads Based on Phthalocyanine−Ruthenium(II) Tris(bipyridine) Complexes. Synthesis and Photoinduced Processes

A new series of multicomponent ZnPc-Ru(bpy)(3) systems, 1a-c, consisting of a zinc-phthalocyanine linked through conjugated and/or nonconjugated connections to a ruthenium(II) tris(bipyridine) complex, has been synthesized. The ruthenium complexes 1a-c were prepared from phthalocyanines 2a-c, bearing a 4-substituted-2,2'-bipyridine ligand by treatment with [Ru(bpy)2Cl2].2H2O. Different synthetic strategies have been devised to prepare the corresponding dyad precursors (2a-c). Compound 2a, for example, with an ethenyl bridge, was synthesized by statistical condensation of 4-tert-butylphthalonitrile and 5-[(E)-2-(3,4-dicyanophenyl)ethenyl]-2,2'-bipyridine (3) in the presence of zinc chloride. Compounds 2b and 2c, having, respectively, an amide or an ethynyl bridge, were prepared following a different synthetic approach. The method involves the coupling of an appropriate 5-substituted-2,2'-bipyridine to an unsymmetrical phthalocyanine suitably functionalized with an amino (4) or an ethynyl group (5). The photophysical properties of the dyads that are ZnPc-Ru(bpy)3 1a-c and related model compounds have been determined by a variety of steady-state (i.e., fluorescence) and time-resolved methods (i.e., fluorescence and transient absorption). Clearly, intramolecular electronic interactions between the two subunits dominate the photophysical events following the initial excitation of either chromophore. These intramolecular interactions lead, in the case of photoexcited ZnPc, to faster intersystem crossing kinetics compared to a ZnPc reference, while photoexcited [Ru(bpy)3]2+) undergoes a rapid and efficient transduction of triplet excited-state energy to the Pc.