The crystal structure of calcium-bound calmodulin (Ca(2+)-CaM) bound to a
peptide analog of the CaM-binding region of chicken smooth muscle myosin light
chain kinase has been determined and refined to a resolution of 2.4 angstroms
(A). The structure is compact and has the shape of an ellipsoid (axial ratio
approximately 2:1). The bound CaM forms a tunnel diagonal to its long axis that
engulfs the helical peptide, with the hydrophobic regions of CaM melded into a
single area that closely covers the hydrophobic side of the peptide. There is a
remarkably high pseudo-twofold symmetry between the closely associated domains.
The central helix of the native CaM is unwound and expanded into a bend between
residues 73 and 77. About 185 contacts (less than 4 A) are formed between CaM
and the peptide, with van der Waals contacts comprising approximately 80% of
this total.
