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Focusing of the electrostatic potential at EF‐hands of calbindin D 9k : Titration of acidic residues
Author(s) -
Kesvatera Tõnu,
Jönsson Bo,
Thulin Eva,
Linse Sara
Publication year - 2001
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.1132
Subject(s) - titration , calmodulin , chemistry , calcium binding protein , aspartic acid , glutamic acid , binding site , ef hand , electrostatics , calbindin , biophysics , crystallography , amino acid , biochemistry , calcium , inorganic chemistry , biology , organic chemistry , enzyme
Biological functions for a large class of calmodulin‐related proteins, such as target protein activation and Ca 2+ buffering, are based on fine‐tuned binding and release of Ca 2+ ions by pairs of coupled EF‐hand metal binding sites. These are abundantly filled with acidic residues of so far unknown ionization characteristics, but assumed to be essential for protein function in their ionized forms. Here we describe the measurement and modeling of pK a values for all aspartic and glutamic acid residues in apo calbindin D 9k , a representative of calmodulin‐related proteins. We point out that while all the acidic residues are ionized predominantly at neutral pH, the onset of proton uptake by Ca 2+ ligands with high pK a under these conditions may have functional implications. We also show that the negative electrostatic potential is focused at the bidental Ca 2+ ligand of each site, and that the potential is significantly more negative at the N‐terminal binding site. Proteins 2001;45:129–135. © 2001 Wiley‐Liss, Inc.