Photoinduced Intramolecular Electron-Transfer Reactions of Reconstituted Met- and Zinc-Myoglobins Appending Acridine and Methylacridinium Ion as DNA-Binders

Synthesis, spectroscopic studies and biological evaluation of acridine derivatives: The role of aggregation on the photodynamic efficiency

Two new photoactive compounds (1 and 2) derived from the 9-amidoacridine chromophore have been synthesized and fully characterized. Their abilities to produce singlet oxygen upon irradiation have been compared. The synthesized compounds show very different self-aggregating properties since only 1 present a strong tendency to aggregate in water. Biological assays were conducted with two cell types: hepatoma cells (Hep3B) and human umbilical vein endothelial cells (HUVEC). Photodynamic therapy (PDT) studies carried out with Hep3B cells showed that non-aggregating compound 2 showed photoxicity, ascribed to the production of singlet oxygen, being aggregating compound 1 photochemically inactive. On the other hand suspensions of 1, characterized as nano-sized aggregates, have notable antiproliferative activity towards this cell line in the dark.

Site-Selective Conjugation of Native Proteins with DNA

Conjugation of DNA to proteins is increasingly used in academia and industry to provide proteins with tags for identification or handles for hybridization to other DNA strands. Assay technologies such as immuno-PCR and proximity ligation and the imaging technology DNA-PAINT require DNA-protein conjugates. In DNA nanotechnology, the DNA handle is exploited to precisely position proteins by self-assembly. For these applications, site-selective conjugation is almost always desired because fully functional proteins are required to maintain the specificity of antibodies and the activity of enzymes. The introduction of a bioorthogonal handle at a specific position of a protein by recombinant techniques provides an excellent approach to site-specific conjugation, but for many laboratories and for applications where several proteins are to be labeled, the expression of recombinant proteins may be cumbersome. In recent years, a number of chemical methods that target conjugation to specific sites at native proteins have become available, and an overview of these methods is provided in this Account. Our laboratory has investigated DNA-templated protein conjugation (DTPC), which offers an alternative approach to site-selective conjugation of DNA to proteins. The method is inspired by the concept of DNA-templated synthesis where functional groups conjugated to DNA strands are preorganized by DNA hybridization to dramatically increase the reaction rate. In DPTC, we target metal binding sites in proteins to template selective covalent conjugation reactions. By chelation of a DNA-metal complex with a metal binding site of the protein, an electrophile on a second DNA strand is aligned for reaction with a lysine side chain on the protein in the proximity of the metal binding site. The method is quite general because approximately one-third of all wild-type proteins contain metal-binding sites, including many IgG antibodies, and it is also applicable to His-tagged proteins. This emerging field provides direct access to site-selective conjugates of DNA to commercially available proteins. In this Account, we introduce these methods to the reader and describe current developments and future aspects.

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.

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.