title: Magnesium promotes structural integrity and conformational switching action of a calcium sensor protein.
abstract: Calcium binding proteins carry out various signal transduction processes upon binding to Ca2+. In general, these proteins perform their functions in a high background of Mg2+. Here, we report the role of Mg2+ on a calcium sensor protein from Entamoeba histolytica (EhCaBP), containing four Ca2+-binding sites. Mg2+-bound EhCaBP exists as a monomer with a conformation different from that of the holo- and apo-EhCaBP. NMR and biophysical data on EhCaBP demonstrate that Mg2+ stabilizes the closed conformation of the apo form. In the presence of Mg2+, the partially collapsed apo-EhCaBP gains stability and structural integrity. Mg2+ binds to only 3 out of 4 calcium binding sites in EhCaBP. The Ca2+ binding affinity and cooperativity of the conformational switching from the "closed" to the "open" state is significantly modulated by the presence of Mg2+. This fine-tuning of the Ca2+ concentration to switch its conformation is essential for CaBPs to carry out the signal transduction process efficiently.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India.
authors.forename: Sulakshana
authors.initials: S
authors.lastname: Mukherjee
authors.forename: P M Krishna
authors.initials: PM
authors.lastname: Mohan
authors.forename: Kandala V R
authors.initials: KV
authors.lastname: Chary
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D004748:Entamoeba histolytica / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry*; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D015800:Protozoan Proteins; C075554:calcium-binding protein, Entamoeba histolytica; D008274:Magnesium; D002118:Calcium