title: Thermodynamics of formation of the insulin hexamer: metal-stabilized proton-coupled assembly of quaternary structure.
abstract: The thermodynamics of formation of the insulin hexamer, which is stabilized by two Zn(2+) ions, were quantified by isothermal titration calorimetry (ITC). Because the insulin monomer is unstable to aggregation (fibrillation) during ITC measurements, an original method involving EDTA chelation of Zn(2+) from the hexamer was employed. The two metal ions are chelated sequentially, reflecting stepwise Zn(2+) binding and stabilization of the quaternary structure. Analysis of the ITC data reveals that two to three H(+) bind to the hexamer upon its formation at pH 7.4, which is both enthalpically and entropically favored. The former is due to Zn(2+) coordination to His residues from three subunits, and the latter is associated with desolvation that accompanies the protonation and the packing of the subunits in the hexamer.
authors: Department of Chemistry, Dartmouth College , 6128 Burke Laboratory, Hanover, New Hampshire 03755, United States.
authors: Margaret C
authors: MC
authors: Carpenter
authors: Dean E
authors: DE
authors: Wilcox
mesh_terms: D006801:Humans; D007328:Insulin / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D055503:Protein Multimerization / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D020836:Protein Structure, Quaternary / Q000187:drug effects; D011522:Protons; D013816:Thermodynamics; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D007328:Insulin; D011522:Protons; D015032:Zinc