title: Energetics and mechanism of Ca2+ displacement by lanthanides in a calcium binding protein.
abstract: The displacement of Ca(2+) by trivalent lanthanide ions (Tm(3+)) in a protozoan (Entamoeba histolytica) Ca(2+) binding protein has been studied by NMR and isothermal calorimetry (ITC). The study provides a basis for understanding the behavior of lanthanides when used as a substitute for Ca(2+), the pattern of sequential binding, the structural changes involved, the range and magnitude of paramagnetic interaction, and the associated energetics and mechanism. The progressive Ca(2+) displacement from site III first, followed by displacement from site II, I, and IV, as observed during the NMR titration experiments, is interpreted in the light of ITC data to provide a deeper insight into the intradomain and, for the first time, interdomain cooperativity and information about the statistical phenomenon involved in it. A theoretical model governing Ca(2+) displacement is provided. The small structural changes involved in Ca(2+) displacement by a diamagnetic lanthanide (La(3+)) has also been monitored.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400 005, India.
authors.forename: Sourajit M
authors.initials: SM
authors.lastname: Mustafi
authors.forename: Sulakshana
authors.initials: S
authors.lastname: Mukherjee
authors.forename: Kandala V R
authors.initials: KV
authors.lastname: Chary
authors.forename: Cristina
authors.initials: C
authors.lastname: Del Bianco
authors.forename: Claudio
authors.initials: C
authors.lastname: Luchinat
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002151:Calorimetry; D028581:Lanthanoid Series Elements / Q000378:metabolism*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D013816:Thermodynamics
chemical_list: D002135:Calcium-Binding Proteins; D028581:Lanthanoid Series Elements; D002118:Calcium