Point amino acid substitutions in the Ca2+-binding sites of recoverin. III. A mutant with the fourth reconstructed Ca2+-binding site

Unlike wild type recoverin with only two (the second and the third) functioning Ca+2-binding sites out of four potential ones, the +EF4 mutant contains a third active Ca+2-binding site. This site was reconstructed from the fourth potential Ca+2-binding domain by the introduction of several amino acid substitutions in it by site-directed mutagenesis. The effect of these mutations in the fourth potential Ca+2-binding site of myristoylated recoverin on the structural features and conformational stability of the protein was studied by fluorimetry and circular dichroism. The apoform of the resulting mutant (free of Ca2+ ions) was shown to have a higher calcium capacity, significantly lower thermal stability, and noticeably different secondary and tertiary structures as compared with the apoform of wild-type recoverin.