A peptide analog of the calmodulin-binding domain of myosin light chain kinase adopts an alpha-helical structure in aqueous trifluoroethanol

Abstract

A 22-residue synthetic peptide encompassing the calmodulin (CaM)-binding domain of skeletal muscle myosin light chain kinase was studied by two-dimensional NMR and CD spectroscopy. In water the peptide does not form any regular structure; however, addition of the helix-inducing solvent trifluoroethanol (TFE) causes it to form an alpha-helical structure. The proton NMR spectra of this peptide in 25% and 40% TFE were assigned by double quantum-filtered J-correlated spectroscopy, total correlation spectroscopy, and nuclear Overhauser effect correlated spectroscopy spectra. In addition, the alpha-carbon chemical shifts were obtained from (1H,13C)-heteronuclear multiple quantum coherence spectra. The presence of numerous dNN(i, i + 1), d alpha N(i, i + 3), and d alpha beta(i, i + 3) NOE crosspeaks indicates that an alpha-helix can be formed from residues 3 to 20; this is further supported by the CD data. Upfield alpha-proton and downfield alpha-carbon shifts in this region of the peptide provide further support for the formation of an alpha-helix. The helix induced by TFE appears to be similar to that formed upon binding of the peptide to CaM.