1H‐NMR studies of calmodulin

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Abstract
Using assignments of resonances in the 1H NMR spectrum of calmodulin obtained by the use of large tryptic fragments of the molecule, the spectral changes which occur on Ca2+ binding to calmodulin were examined in detail. Ca2+ binding occurs in 2 stages: the first 2 Ca2+ ions bind at sites III and IV (numbered from the N terminus) and the second 2 Ca2+ ions bind at sites I and II. The high-affinity binding causes perturbations of residues in both halves of the molecule, whereas binding at the 2 N-terminal sites only affects sidechains in that half of the molecule. The effects of binding Cd2+ to the Ca2+-binding sites of calmodulin were also studied by 1H NMR. The cation induces spectral changes which are very similar to those seen for Ca2+, but some important differences do exist.