Point amino acid substitutions in the Ca2+-binding sites of recoverin. II.The unusual behavior of the protein upon the binding of calcium ions

The structural properties of myristoylated forms of recombinant recoverin o f the wild type and of its mutants with damaged second and/or third Ca2+-bi nding sites were studied by fluorimetry and circular dichroism. The interac tion of wild-type recoverin with calcium ions was shown to induce unusual s tructural rearrangements in its molecule. In particular, protein binding wi th Ca2+ ions results in an increase in the mobility of the environment of T rp residues, in higher hydrophobicity, and in elevated thermal stability (i ts thermal transition shifts by 15 degrees C to higher temperatures) but ha s almost no effect on its secondary structure. Similar structural changes i nduced by Ca2+ are also characteristic of the -EF2 mutant of recoverin whos e second Ca2+-binding site is modified and cannot bind calcium ions. The st ructural properties of the -EF3 and -EF2,3 mutants (whose third or simultan eously second and third Ca2+-binding sites, respectively, are modified and damaged) are practically indifferent to calcium ions.