Circular Dichroism Spectroscopy
Circular dichroism (CD), is the differential absorption of left- and right-handed circularly polarized light which arises dye to the asymmetry of naturally occurring molecules such as proteins and sugars. The CD spectrum is the wavelength dependency of the difference in absorption between the right and left-handed components.
CD spectroscopy is particularly good for characterising protein secondary and tertiary structure, for comparing the structures of proteins from different manufacturing processes, formulations or mutations and for studying the effects of temperature, pH, denaturants and the effect of other additives or interactions such as ligand binding on protein structure.
CD spectra measured in the near ultra-violet (250-350 nm) provide a fingerprint of the chiral environment of tryptophan (280-300nm), tyrosine (270-290nm) and phenylalanine (250-270nm) residues so the tertiary structure of proteins in solution.
In contrast the information obtained from far ultra-violet CD spectroscopy (200-250 nm) is related to the secondary structure of proteins. Features in the far-UV CD spectra are fitted using model peptide and protein spectra to determine the relative proportions of a molecule that is in the alpha-helix conformation, the beta-sheet conformation, the beta-turn conformation, or some other (random) conformation.
Facilities:
Avacta facilities include the JASCO J-810 Spectropolarimeter for recording Circular Dichroism measurements.
References
- Circular Dichroism and Linear Dichroism, A. Rodger and B. Norden (1997) Oxford University Press, Oxford, New York, Tokyo.
- Circular Dichroism and Optical Rotatory Dispersion of Proteins and Polypeptides, A.J. Alder, N.J. Greenfield and G.D. Fasman (1973) Methods Enzymology, 27, 675
- Computed Circular Dichroism Spectra for the Evaluation of Protein Conformation, N. Greenfield and G.D. Fasman (1996) Biochemistry, 8, 4108
- Protein Secondary Structure and Circular Dichroism: A Practical Guide, W.C. Johnson, (1990) Proteins, 7, 205