title: Thermodynamics of Zn2+ binding to Cys2His2 and Cys2HisCys zinc fingers and a Cys4 transcription factor site.
abstract: The thermodynamics of Zn(2+) binding to three peptides corresponding to naturally occurring Zn-binding sequences in transcription factors have been quantified with isothermal titration calorimetry (ITC). These peptides, the third zinc finger of Sp1 (Sp1-3), the second zinc finger of myelin transcription factor 1 (MyT1-2), and the second Zn-binding sequence of the DNA-binding domain of glucocorticoid receptor (GR-2), bind Zn(2+) with Cys(2)His(2), Cys(2)HisCys, and Cys(4) coordination, respectively. Circular dichroism confirms that Sp1-3 and MyT1-2 have considerable and negligible Zn-stabilized secondary structure, respectively, and indicate only a small amount for GR-2. The pK(a)'s of the Sp1-3 cysteines and histidines were determined by NMR and used to estimate the number of protons displaced by Zn(2+) at pH 7.4. ITC was also used to determine this number, and the two methods agree. Subtraction of buffer contributions to the calorimetric data reveals that all three peptides have a similar affinity for Zn(2+), which has equal enthalpy and entropy components for Sp1-3 but is more enthalpically disfavored and entropically favored with increasing Cys ligands. The resulting enthalpy-entropy compensation originates from the Zn-Cys coordination, as subtraction of the cysteine deprotonation enthalpy results in a similar Zn(2+)-binding enthalpy for all three peptides, and the binding entropy tracks with the number of displaced protons. Metal and protein components of the binding enthalpy and entropy have been estimated. While dominated by Zn(2+) coordination to the cysteines and histidines, other residues in the sequence affect the protein contributions that modulate the stability of these motifs.
authors.affiliation: Department of Chemistry, Dartmouth College Hanover, New Hampshire 03755, USA
authors.forename: Anne M
authors.initials: AM
authors.lastname: Rich
authors.forename: Elisa
authors.initials: E
authors.lastname: Bombarda
authors.forename: Austin D
authors.initials: AD
authors.lastname: Schenk
authors.forename: Paul E
authors.initials: PE
authors.lastname: Lee
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Cox
authors.forename: Anne M
authors.initials: AM
authors.lastname: Spuches
authors.forename: Lynn D
authors.initials: LD
authors.lastname: Hudson
authors.forename: Bruno
authors.initials: B
authors.lastname: Kieffer
authors.forename: Dean E
authors.initials: DE
authors.lastname: Wilcox
mesh_terms: D002942:Circular Dichroism; D003545:Cysteine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D055550:Protein Stability; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*; D016335:Zinc Fingers
chemical_list: D015032:Zinc; D003545:Cysteine