Biophys J, September 2002, p. 1455-1464, Vol. 83, No. 3

Dynamic Light Scattering Study of Calmodulin-Target Peptide Complexes

Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada

Dynamic light scattering (DLS) has been used to assess the influence of eleven different synthetic peptides, comprising the calmodulin (CaM)-binding domains of various CaM-binding proteins, on the structure of apo-CaM (calcium-free) and Ca²⁺-CaM. Peptides that bind CaM in a 1:1 and 2:1 peptide-to-protein ratio were studied, as were solutions of CaM bound simultaneously to two different peptides. DLS was also used to investigate the effect of Ca²⁺ on the N- and C-terminal CaM fragments TR1C and TR2C, and to determine whether the two lobes of CaM interact in solution. The results obtained in this study were comparable to similar solution studies performed for some of these peptides using small-angle x-ray scattering. The addition of Ca²⁺ to apo-CaM increased the hydrodynamic radius from 2.5 to 3.0 nm. The peptides studied induced a collapse of the elongated Ca²⁺-CaM structure to a more globular form, decreasing its hydrodynamic radius by an average of 25%. None of the peptides had an effect on the conformation of apo-CaM, indicating that either most of the peptides did not interact with apo-CaM, or if bound, they did not cause a large conformational change. The hydrodynamic radii of TR1C and TR2C CaM fragments were not significantly affected by the addition of Ca²⁺. The addition of a target peptide and Ca²⁺ to the two fragments of CaM, suggest that a globular complex is forming, as has been seen in nuclear magnetic resonance solution studies. This work demonstrates that dynamic light scattering is an inexpensive and efficient technique for assessing large-scale conformational changes that take place in calmodulin and related proteins upon binding of Ca²⁺ ions and peptides, and provides a qualitative picture of how this occurs. This work also illustrates that DLS provides a rapid screening method for identifying new CaM targets.

Biophys J, September 2002, p. 1455-1464, Vol. 83, No. 3
© 2002 by the Biophysical Society   0006-3495/02/09/1455/10  $2.00

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