title: Thermodynamics of Pb(ii) and Zn(ii) binding to MT-3, a neurologically important metallothionein.
abstract: Isothermal titration calorimetry (ITC) was used to quantify the thermodynamics of Pb(2+) and Zn(2+) binding to metallothionein-3 (MT-3). Pb(2+) binds to zinc-replete Zn7MT-3 displacing each zinc ion with a similar change in free energy (ΔG) and enthalpy (ΔH). EDTA chelation measurements of Zn7MT-3 and Pb7MT-3 reveal that both metal ions are extracted in a tri-phasic process, indicating that they bind to the protein in three populations with different binding thermodynamics. Metal binding is entropically favoured, with an enthalpic penalty that reflects the enthalpic cost of cysteine deprotonation accompanying thiolate ligation of the metal ions. These data indicate that Pb(2+) binding to both apo MT-3 and Zn7MT-3 is thermodynamically favourable, and implicate MT-3 in neuronal lead biochemistry.
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA. dwilcox@dartmouth.edu.
authors.forename: M C
authors.initials: MC
authors.lastname: Carpenter
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
authors.forename: A
authors.initials: A
authors.lastname: Shami Shah
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
authors.forename: S
authors.initials: S
authors.lastname: DeSilva
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
authors.forename: A
authors.initials: A
authors.lastname: Gleaton
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
authors.forename: A
authors.initials: A
authors.lastname: Su
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA.
authors.forename: B
authors.initials: B
authors.lastname: Goundie
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA. dwilcox@dartmouth.edu.
authors.forename: M L
authors.initials: ML
authors.lastname: Croteau
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA. dwilcox@dartmouth.edu.
authors.forename: M J
authors.initials: MJ
authors.lastname: Stevenson
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA. dwilcox@dartmouth.edu.
authors.forename: D E
authors.initials: DE
authors.lastname: Wilcox
authors.affiliation: Department of Chemistry, Bates College, Lewiston, ME 04240, USA and Department of Chemistry, Barnard College, Columbia University, NY, NY 10027, USA. raustin@barnard.edu.
authors.forename: R N
authors.initials: RN
authors.lastname: Austin
mesh_terms: D006801:Humans; D007700:Kinetics; D007854:Lead / Q000378:metabolism*; D008668:Metallothionein / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D011485:Protein Binding; D013816:Thermodynamics; D015032:Zinc / Q000378:metabolism*
chemical_list: D007854:Lead; D008668:Metallothionein; D015032:Zinc