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| - Toward Ligand Identification within a CCHHC Zinc-Binding Domain from the NZF/MyT1Family
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| - A family of proteins that contain domains with the sequence Cys−X4−Cys−X4−His−X7−His−X5−Cys has been identified. A peptide corresponding to such a domain has been synthesized and characterized. The spectroscopic properties of the cobalt(II) complex demonstrate that metal binding is tetrahedral with coordination by three cysteinates and one histidine. Further analysis of mutated peptides suggests that either of the two conserved histidine residues can participate in metal binding.
- A family of proteins that contain presumed zinc-binding domains with the consensus sequence Cys−X4−Cys-X4−His-X7−His-X5−Cys has recently been identified, but the metal binding and structural properties of thesedomains have not been investigated. This consensus is striking because of the presence of five conserved potentialzinc-binding residues. A peptide corresponding to the third putative zinc-binding domain from the transcriptionfactor NZF-1 (hereafter NZF-13) has been synthesized and characterized. The UV−visible absorption spectroscopicproperties of the cobalt(II) complex of this peptide demonstrate that metal binding is tetrahedral, and the positionof the visible absorption bands suggests coordination by three cysteinates and one histidine. To identify which ofthe two conserved histidine residues acts a metal-binding residue, two histidine to alanine variant peptides werealso synthesized. Both variant peptides bound cobalt(II) in a tetrahedral fashion; replacement of the first of thetwo histidines has a somewhat larger effect on the detailed shape of the absorption spectral features than doesreplacement of the second histidine. These results suggest that the metal-coordinating residues (italicized) areCys−X4−Cys−X4−His−X7−His−X5−Cys. However, simultaneous substitution of both histidine residues withalanine generated a peptide with much more dramatically affected metal binding properties. These observationssuggests that the relatively modest effects observed for the singly substituted peptides may be due to metalinteractions involving the remaining histidine. Because of these phenomena, further studies will be required toestablish more conclusively the roles of the two histidine residues in metal binding and the potential significanceof the apparent alternative histidine coordination.
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