Effects of DNA binding of the zinc finger and linkers for domain fusion on the catalytic activity of sequence-specific chimeric recombinases determined by a facile fluorescent system.

Artificial zinc finger proteins (ZFPs) consist of Cys(2)-His(2)-type modules composed of ∼30 amino acids with a ßßα structure that coordinates a zinc ion. ZFPs that recognize specific DNA target sequences can substitute for the binding domains of enzymes that act on DNA to create designer enzymes with programmable sequence specificity. The most studied of these engineered enzymes are zinc finger nucleases (ZFNs). ZFNs have been widely used to model organisms and are currently in human clinical trials with an aim of therapeutic gene editing. Difficulties with ZFNs arise from unpredictable mutations caused by nonhomologous end joining and off-target DNA cleavage and mutagenesis. A more recent strategy that aims to address the shortcomings of ZFNs involves zinc finger recombinases (ZFRs). A thorough understanding of ZFRs and methods for their modification promises powerful new tools for gene manipulation in model organisms as well as in gene therapy. In an effort to design efficient and specific ZFRs, the effects of the DNA binding affinity of the zinc finger domains and the linker sequence between ZFPs and recombinase catalytic domains have been assessed. A plasmid system containing ZFR target sites was constructed for evaluation of catalytic activities of ZFRs with variable linker lengths and numbers of zinc finger modules. Recombination efficiencies were evaluated by restriction enzyme analysis of isolated plasmids after reaction in Escherichia coli and changes in EGFP fluorescence in mammalian cells. The results provide information relevant to the design of ZFRs that will be useful for sequence-specific genome modification.

Bivalent ligands of CXCR4 with rigid linkers for elucidation of the dimerization state in cells.

To date, challenges in the design of bivalent ligands for G protein-coupled receptors (GPCRs) have revealed difficulties stemming from lack of knowledge of the state of oligomerization of the GPCR. The synthetic bivalent ligands with rigid linkers that are presented here can predict the dimer form of CXCR4 and be applied to molecular probes in cancerous cells. This "molecular ruler" approach would be useful in elucidating the details of CXCR4 oligomer formation.

Development of crosslink-type tag-probe pairs for fluorescent imaging of proteins.

Useful methods of protein labeling via functional peptide tags have been developed in the field of proteome and chemical biology. New tag-probe pairs based on leucine zipper peptides for labeling target proteins are described. These consist of an α-helical probe peptide with an environmental-sensitive fluorescent dye and two antiparallel α-helical tag peptides, and may be crosslinked, from the Cys residue of the tag peptide to the N(α)-chloroacetyl group of the probe peptide. Binding of the probe peptide to the tag peptides results in movement of the fluorophore from a hydrophilic to a hydrophobic environment inside the leucine zipper structure, causing a dramatic fluorescent change, mediated by the binding of the two peptides. As a spacer between the N(α)-chloroacetyl group and the original probe sequence, a single Gly residue was the most suitable among 0-2 Gly residues. Crosslinking leads to superior fluorescence response, binding affinity, and chemical stability. These ZIP tag-probe pairs are useful for labeling and fluorescent imaging of proteins.