Structural basis for the negative allostery between Ca(2+)- and Mg(2+)-binding in the intracellular Ca(2+)-receptor calbindin D9k.
The three-dimensional structures of the magnesium- and manganese-bound forms of calbindin D9k were determined to 1.6 A and 1.9 A resolution, respectively, using X-ray crystallography. These two structures are nearly identical but deviate significantly from both the calcium bound form and the metal ion-free (apo) form. The largest structural differences are seen in the C-terminal EF-hand, and involve changes in both metal ion coordination and helix packing. The N-terminal calcium binding site is not occupied by any metal ion in the magnesium and manganese structures, and shows little structural deviation from the apo and calcium bound forms. 1H-NMR and UV spectroscopic studies at physiological ion concentrations show that the C-terminal site of the protein is significantly populated by magnesium at resting cell calcium levels, and that there is a negative allosteric interaction between magnesium and calcium binding. Calcium binding was found to occur with positive cooperativity at physiological magnesium concentration.
Andersson
M
M
Department of Molecular Biophysics, Lund University, Sweden.
Malmendal
A
A
Linse
S
S
Ivarsson
I
I
Forsén
S
S
Svensson
L A
LA
D000494:Allosteric Regulation; D064026:Calbindins; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D008274:Magnesium / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D011487:Protein Conformation; D064030:S100 Calcium Binding Protein G / Q000737:chemistry* / Q000378:metabolism
D064026:Calbindins; D002413:Cations, Divalent; D064030:S100 Calcium Binding Protein G; D008274:Magnesium; D002118:Calcium