catena-Poly[[(5,5'-dimethyl-2,2'-bi-pyridine-κN,N')cadmium(II)]-di-μ-iodido]

Metal-ion-regulated miniature DNA-binding proteins based on GCN4 and non-native regulation sites

The design of artificial peptide dimers containing polypyridine switching domains, for which metal-ion coordination is shown to regulate DNA binding, is reported. Short peptides, based on the basic domain of the GCN4 transcription factor (GCN4bd), dimerised with either 2,2'-bipyridine (bipy(GCN4bd)2 ) or 2,2':6',2''-terpyridine (terpy(GCN4bd)2 ) linker units, undergo a conformational rearrangement on Cu(II) and Zn(II) coordination. Depending on the linker substitution pattern, this is proposed to alter the relative alignment of the two peptide moieties, and in turn regulate DNA binding. Circular dichroism and UV-visible spectroscopy reveal that Cu(II) and Zn(II) coordination promotes binding to DNA containing the CRE target site, but to a differing and opposite degree for the two linkers, and that the metal-ion affinity for terpy(GCN4bd)2 is enhanced in the presence of CRE DNA. Binding to DNA containing the shorter AP1 target site, which lacks a single nucleobase pair compared to CRE, as well as half-CRE, which contains only half of the CRE target site, was also investigated. Cu(II) and Zn(II) coordination to terpy(GCN4bd)2 promotes binding to AP1 DNA, and to a lesser extent half-CRE DNA. Whereas, bipy(GCN4bd)2 , for which interpeptide distances are largely independent of metal-ion coordination and less suitable for binding to these shorter sites, displays allosteric ineffective behaviour in these cases. These findings for the first time demonstrate that biomolecular recognition, and specifically sequence-selective DNA binding, can be controlled by metal-ion coordination to designed switching units, non-native regulation sites, in artificial biomolecules. We believe that in the future these could find a wide range of applications in biotechnology.

Conformational Study of an Artificial Metal-Dependent Regulation Site for Use in Designer Proteins

This report describes the dimerisation of glutathione, and by extension, other cysteine-containing peptides or protein fragments, with a 5, 5'-disubstituted-2, 2'-bipyridine or 6, 6"-disubstituted-2, 2':6',2"-terpyridine unit. The resulting bipy-GS2 and terpy-GS2 were investigated as potential metal ion dependent switches in aqueous solution, and were found to predominantly adopt the transoïd conformation at physiological pH. Metal complexation with CuII and ZnII at this pH has been studied by UV/Vis, CD, NMR and ion-mobility mass spectrometry. ZnII titrations are consistent with the formation of a 1:1 ZnII:terpy-GS2 complex at pH 7.4, but bipy-GS2 was shown to form both 1:1 and 1:2 complexes with the former being predominant under dilute micromolar conditions. Formation constants for the resulting 1:1 complexes were determined to be log KM 6.86 (bipy-GS2 ) and 6.22 (terpy-GS2 ), consistent with a higher affinity for the unconstrained bipyridine, compared to the strained terpyridine. CuII coordination involves the initial formation of 1:1 complexes, followed by 1.5Cu:1bipy-GS2 and 2Cu:1terpy-GS2 complexes at micromolar concentrations. Binding constants for formation of the 1:1 complexes (log KM 12.5 (bipy-GS2 ); 8.04 and 7.14 (terpy-GS2 )) indicate a higher affinity for CuII than ZnII. Finally, ion-mobility MS studies detected the free ligands in their protonated form, and were consistent with the formation of two different Cu adducts with different conformations in the gas-phase. We illustrate that the bipyridine and terpyridine dimerisation units can behave like conformational switches in response to Cu/Zn complexation, and propose that in future these can be employed in synthetic biology with larger peptide or protein fragments, to control large scale folding and related biological function.

catena-Poly[[(5,5'-dimethyl-2,2'-bipyridine-κ(2)N,N')cadmium]-di-μ-bromido]

In the crystal of the title polymeric compound, [CdBr₂(C₁₂H₁₂N₂)]_n, the Cd^II cation is located on a twofold rotation axis. The Cd^II cation is six-coordinated in a distorted octa­hedral geometry formed by two N atoms from the 5,5′-dimethyl-2,2′-bipyridine ligand and four bridging Br⁻ anions. The bridging function of the Br⁻ anions leads to a polymeric chain running along the c axis.

catena-Poly[[aqua-(5,5'-dimethyl-2,2'-bipyridine-κN,N')copper(II)]-μ-2,2'-oxydibenzoato-κO:O']

In the title compound, [Cu(C₁₄H₈O₅)(C₁₂H₁₂N₂)(H₂O)]_n, the Cu^II ion is penta­coordinated in a square-pyramidal geometry. Two N atoms of the chelating 5,5′-dimethyl-2,2′-bipyridine (dbp) ligand and two O atoms of two different 2,2′-oxydibenzoic (odb) ligands occupy the basal plane while the water O atom completes the square-pyramidal geometry at the apical site. The non-water N₂O₂ donor atoms are nearly coplanar, with a mean deviation from the least-squares plane of 0.0518 (11) Å and the Cu atom is displaced by 0.1507 (11) Å from this plane towards the apical water O atom. Further coordination via the 2,2′-oxydibenzoate anions forms a one-dimensional coordination polymer extending parallel to [010]. In the crystal structure, O—H⋯O hydrogen bonds link the mol­ecules into a two-dimensional supra­molecular structure.