Studies of the calmodulin-binding site of twitchin with synthetic peptides using fluorescence and CD spectroscopy

The calcium-dependent interaction of two synthetic peptides derived from the putative calmodulin-binding site in the protein kinase autoinhibitory region of twitchin was studied by fluorescence and CD spectroscopy. The peptides interacted with dansylcalmodulin in the presence of Ca²⁺ as shown by a change in the fluorescence emission spectra. Fluorescence titration of dansylcalmodulin with the peptides was used to quantify this interaction. The peptides appeared to assume a helical conformation in a non-polar environment as seen by CD spectroscopy. The ellipticity of Ca²⁺ calmodulin was enhanced in the presence of peptides compared with that of Ca²⁺ calmodulin and peptides alone, indicating that the peptides had formed a complex with calmodulin. These results support the assignment of the twitchin calmodulin-binding site.