With the success in studying 1:1 protein:metal ion binding, we applied PLIMSTEX to the more challenging 1:4 protein:metal ion binding of calmodulin and Ca2+ binding. Calmodulin, a small (@17 kDa), acidic, and highly conserved protein, is regulated by Ca2+ binding in most eukaryotic cells. When binding Ca2+, calmodulin undergoes conformational changes that enable it to bind to and activate other target proteins, an action that is critical to various aspects of cell metabolism [45, 46]. We wished to learn whether PLIMSTEX can determine the conformational changes, binding stoichiometry, and binding constants for Ca2+ interactions with calmodulin (CaM) under varying conditions of electrolyte identity and ionic strength .
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