Spectroscopic Elucidation of the Inhibitory Mechanism of Cys₂His₂ Zinc Finger Transcription Factors by Cobalt(III) Schiff Base Complexes

Abstract

Transcription factors are key regulators in both normal and pathological cell processes. Affecting the activity of these proteins is a promising strategy for understanding gene regulation and developing effective therapeutics. CoIII Schiff base complexes ([Co(acacen)(L)2]+ where L = labile axial ligands) have been shown to be potent inhibitors of a number of zinc metalloproteins including Cys2His2 zinc finger transcription factors. Inhibition by [Co(acacen)(L)2]+ of the target protein is believed to occur through a dissociative exchange of the labile axial ligands for histidine (His) residues essential for function. Here, we report a series of spectroscopic investigations with model peptides of zinc fingers that elucidate the interaction between [Co(acacen)(L)2]+ complexes and zinc finger transcription factors. Observed changes in NMR chemical shifts and 2D 1H-1H NOESY NMR spectra demonstrate the preference of [Co(acacen)(L)2]+ complexes to coordinate His residues over other amino acids. The conformation of [Co(acacen)(L)2]+ upon His-coordination was characterized by 1H NMR, near-UV circular dichroism, and electronic absorption. These studies reveal that the resulting His-coordinated [Co(acacen)(L)2]+ complex possesses an octahedral structure. The effects of [Co(acacen)(L)2]+ complexes on the zinc finger structure were assessed by the degree of hydrogen bonding (probed by 2D NMR) and secondary structure profiles measured by far-UV circular dichroism. These structural studies demonstrate the ability of [Co(acacen)(L)2]+ complexes to disrupt the ββα structure of zinc fingers, resulting in primarily random coil conformations. A mechanism is described wherein [Co(acacen)(L)2]+ complexes inhibit zinc finger transcription factor activity through selectively coordinating His residues in the zinc finger via dissociative ligand exchange and disrupting the ββα structural motif required for gene regulation.

Cancer of the Pancreas: Molecular Pathways and Current Advancement in Treatment

“…A cobalt (III) Schiff base complexe ([Co(acacen)(NH 3 ) 2 ] + ) has been shown to inhibit C 2 H 2 zinc finger transcription factors non-specifically. To enhance the specificity, an E-box DNA oligonucleotide specifically targeting Snail was attached to the acacen equatorial ligand 77 . This Co(III)-E-box complex was a potent inhibitor of Snail- mediated transcriptional repression in breast cancer cells and in the neural crest of Xenopus 78 .…”

Targeting MYC in cancer therapy: RNA processing offers new opportunities

“…Other transcription factors have been targeted by similar strategies based on directly or indirectly preventing protein:protein or protein:DNA interactions. For example, S3I‐201 prevents the dimerization of Stat3 and the binding of Stat3 to DNA , and Co III Schiff base complexes can alter the structure of zinc fingers, which are a common feature of transcription factors, and selectively disrupt their DNA‐binding ability .…”

Metal complexes of amino acids and peptides

“…It was also demonstrated that in neutral samples Hg(II) can completely replaces Zn(II) in these complexes. 323 Because of the possible redox reactions and concomitant complex formation Cu(II) ions are also potential inhibitors of zinc finger peptides. The results were simulated by a multisite binding model with a significant interaction between them.…”