Circular dichroism (CD)

What is CD analysis?
Circular dichroism (CD) spectroscopy measures the difference in the absorption of left-handed circularly polarised light (L-CPL) and right-handed circularly polarised light (R-CPL) which occurs due to the structural asymmetry of molecule. The CD spectrum of a molecule obtained by CD spectroscopy is useful in learning the structure of biological macromolecules which are usually chiral molecules. CD spectroscopy is used for evaluating the secondary and tertiary structure of proteins.


How to determine the protein structure by CD?
The secondary structure of proteins consists of different elements including α-helixes, β-pleated sheets, turns and random coils, which show charateristic CD spectra. The α-helix has negative bands at 222 nm and 208 nm respectively and a positive band at 193 nm. The β-pleated sheet (β-helices) shows a negative band at 218 nm and a positive band at 195 nm. And the random coil has a low ellipticity above 210 nm and a negative band near 195 nm. Therefore analysis of CD spectra in the far ultraviolet wavelength region (far-UV, 190-280 nm) leads to estimate the secondary structural composition of proteins.

The tertiary structure information of a protein can be obtained from the CD spectrum in near ultraviolet wavelength region (near-UV, 250-350 nm). Aromatic amino acids have chromophores and show characteristic wavelength profile: phenylalanine residues have a sharp peak between 255-270 nm; tyrosine shows a peak from 275-282 nm; and tryptophan has a peak between 290-305 nm. In addition, an absorption by disulfide bonds occurs near 260 nm and is broad weak signals throughout the near-UV spectrum.
Pronalyse offers overall scanning and data analysis of your proteins of interest in far-UV and near-UV region for the secondary and tertiary structures, and the structural changes resulted from its sequence or environment.

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