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Circular Dichroism: Studies of Proteins

  1. Sharon M Kelly,
  2. Nicholas C Price

Published Online: 15 DEC 2009

DOI: 10.1002/9780470015902.a0003043.pub2



How to Cite

Kelly, S. M. and Price, N. C. 2009. Circular Dichroism: Studies of Proteins. eLS. .

Author Information

  1. University of Glasgow, Scotland, UK

Publication History

  1. Published Online: 15 DEC 2009


Circular dichroism (CD) is the differential absorption of the left- and right-circularly polarized components of plane-polarized electromagnetic radiation. It can provide structural and dynamic information about biological macromolecules, particularly proteins. The CD spectra in the far-UV (typically 180–240 nm) can give reliable quantitative estimates of the proportions of secondary structural features (helix, sheet, turn, etc.) present in proteins. The spectra in the near-UV (260–320 nm) can be used to explore the environments of aromatic amino acid side-chains and hence to give a measure of tertiary structure. Although CD cannot provide the high-resolution structural data available from X-ray crystallography or nuclear magnetic resonance, its convenience and applicability under a wide variety of experimental conditions make it the technique of choice in many applications, including exploring protein–ligand interactions, conformational changes and protein folding.

Key concepts:

  • Circular dichroism (CD) refers to the difference in absorption of the two components (left- and right-circularly polarized) of plane-polarized radiation.

  • CD is observed when the absorbing molecule or group exhibits chirality (optical activity).

  • Protein structures are chiral and so give rise to CD signals.

  • CD can be used to explore protein structures under a wide range of experimental conditions.

  • The relatively small CD signals observed from proteins mean that care must be taken to gather reliable experimental data.

  • CD signals from proteins in the far-UV and near-UV can be used to explore their secondary and tertiary structures, respectively.

  • CD is an ideal technique to monitor conformational changes in proteins which occur on binding to other molecules.

  • CD can be used to assess the extents of protein unfolding (denaturation) and of refolding of denatured proteins.


  • protein folding;
  • protein unfolding;
  • conformational changes;
  • secondary structure;
  • tertiary structure