Abstract
Sequence homology of the Escherichia coli YiiP places it within the family of cation diffusion facilitators, a family of membrane transporters that play a central role in regulating cellular zinc homeostasis. Here we describe the first thermodynamic and mechanistic studies of metal binding to a cation diffusion facilitator. Isothermal titration calorimetric analyses of the purified YiiP and binding competitions among Zn2+, Cd2+, and Hg2+ revealed a mutually competitive binding site common to three metal ions and a set of noncompetitive binding sites, including one Cd2+ site, one Hg2+ site, and at least one Zn 2+ site, to which the binding of Zn2+ exhibited partial inhibitions of both Cd2+ and Hg2+ bindings. Lowering the pH from 7.0 to 5.5 inhibited binding of Zn2+ and Cd2+ to the common site. Further, the enthalpy change of the Cd2+ binding to the common site was found to be related linearly to the ionization enthalpy of the pH buffer with a slope corresponding to the release of 1.28 H+ for each Cd2+ binding. These H+ effects are consistent with a coupled deprotonation process upon binding of Zn2+ and Cd 2+. Modification of histidine residues by diethyl pyrocarbonate specifically inhibited Zn2+ binding to the common binding site, indicating that the mechanism of binding-deprotonation coupling involves a histidine residue(s).
Original language | English (US) |
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Pages (from-to) | 17173-17180 |
Number of pages | 8 |
Journal | Journal of Biological Chemistry |
Volume | 279 |
Issue number | 17 |
DOIs | |
State | Published - Apr 23 2004 |
Externally published | Yes |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology