Conformational changes upon calcium binding and phosphorylation in a synthetic fragment of calmodulin

We have recently investigated by far‐UV circular dichroism (CD) the effects of Ca2+ binding and the phosphorylation of Ser 81 for the synthetic peptide CaM [54–106] encompassing the Ca2+‐binding loops II and III and the central α helix of calmodulin (CaM) (Arrigoni et al., Biochemistry 2004, 43, 12788–12798). Using computational methods, we studied the changes in the secondary structure implied by these spectra with the aim to investigate the effect of Ca2+ binding and the functional role of the phosphorylation of Ser 81 in the action of the full‐length CaM. Ca2+ binding induces the nucleation of helical structure by inducing side chain stacking of hydrophobic residues. We further investigated the effect of Ca2+ binding by using near‐UV CD spectroscopy. Molecular dynamics simulations of different fragments containing the central α‐helix of CaM using various experimentally determined structures of CaM with bound Ca2+ disclose the structural effects provided by the phosphorylation of Ser 81. This post‐translational modification is predicted to alter the secondary structure in its surrounding and also to hinder the physiological bending of the central helix of CaM through an alteration of the hydrogen bond network established by the side chain of residue 81. Using quantum mechanical methods to predict the CD spectra for the frames obtained during the MD simulations, we are able to reproduce the relative experimental intensities in the far‐UV CD spectra for our peptides. Similar conformational changes that take place in CaM [54–106] upon Ca2+ binding and phosphorylation may occur in the full‐length CaM. © 2006 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 373–385, 2007. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com