title: Thermodynamic analysis of calcium and magnesium binding to calmodulin.
abstract: To elucidate some aspects still debated concerning the interaction of Ca2+ and Mg2+ with CaM, the thermodynamic binding parameters of Ca2+-CaM and Mg2+-CaM complexes were characterized by flow dialysis and isothermal microcalorimetry under different experimental conditions. In particular, the enthalpy and entropy changes associated with Ca2+ and Mg2+ binding to their sites were determined, allowing a better understanding of the mechanism underlying cation-CaM interactions. Ca2+-CaM interaction follows an enthalpy-entropy compensation relationship, suggesting that CaM explores a subspace of isoenergetical conformations which is modified by Ca2+ binding. This Ca2+-induced change in CaM dynamics is proposed to play a key role in CaM function, i.e. in its interaction with and/or activation of target proteins. Furthermore, data show that Mg2+ does not act as a direct competitor for Ca2+ binding on the four main Ca2+ binding sites, but rather as an allosteric effector. This implies that the four main Mg2+ binding sites are distinct from the EF-hand Ca2+ binding sites. Finally, Ca2+ is shown to interact with auxiliary binding sites on CaM. These weak affinity sites were thermodynamically characterized. The results presented here challenge the current accepted view of CaM ion binding.
authors.affiliation: Faculté de Pharmacie, UPRESA CNRS 6032, Marseille, France.
authors.forename: R
authors.initials: R
authors.lastname: Gilli
authors.forename: D
authors.initials: D
authors.lastname: Lafitte
authors.forename: C
authors.initials: C
authors.lastname: Lopez
authors.forename: M
authors.initials: M
authors.lastname: Kilhoffer
authors.forename: A
authors.initials: A
authors.lastname: Makarov
authors.forename: C
authors.initials: C
authors.lastname: Briand
authors.forename: J
authors.initials: J
authors.lastname: Haiech
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D002151:Calorimetry / Q000379:methods; D003956:Dialysis; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D002147:Calmodulin; D008274:Magnesium; D002118:Calcium