The interaction of calmodulin and polylysine as studied by ¹H NMR spectroscopy and sedimentation equilibrium centrifugation

The effects of polylysine on calmodulin were assessed using ¹H NMR and sedimentation equilibrium centrifugation. Sedimentation equilibrium centrifugation measurements demonstrated that calmodulin associates with polylysine at calmodulin:polylysine molar ratios ranging from 10:1 to 2.5:1 and when polylysine is increased above the molar ratio of 1:1 a precipitate is formed. At a 1:2.5 calmodulin:polylysine molar ratio, 75% of the calmodulin precipitates from the solution and virtually no polylysine is present in the precipitate. ¹H NMR studies of ihe aromatic region of calmodulin identified chemical shifts of three peaks at a calmodulin:polylysine molar ratio of 1:1. These studies suggest that polylysine associates with calmodulin in aqueous solution and can alter the structure of calmodulin to cause calmodulin self-aggregation.