Circular Dichroism Spectroscopy Analysis of Protein Secondary Structure

Circular Dichroism (CD) is a widely used method for the study of protein secondary structure and its changes. By analyzing the CD spectrum of a protein, we can obtain a rough composition and distribution of its secondary structure.

 

The Secondary Structure of the Protein

1. α-Helices (Alpha Helices)

This is a right-handed helical structure, which usually shows negative peaks at about 222 nm and 208 nm in the CD spectrum.

 

2. β-Sheets (Beta Sheets)

β-Sheets can be parallel or antiparallel. They show positive peaks at about 218 nm in the CD spectrum and negative peaks at about 210-216 nm.

 

3. β-Turns (Beta Turns)

These structures usually do not produce very obvious peaks in the CD spectrum, but they can be identified by their absence in other secondary structures.

 

4. Random Coils or Unstructured Regions

These areas show negative peaks at about 195 nm in the CD spectrum.

 

Considerations for Using CD to Study Protein Secondary Structure

CD spectra are mainly conducted in the ultraviolet (UV, about 190-250 nm) region, because the secondary structure of proteins has specific spectral features in this area. To obtain accurate secondary structure information, it is necessary to ensure that the sample is pure, and the appropriate solvent and concentration are also important. By comparing CD spectra under different conditions (such as different temperatures, pH or presence of ligands), the stability and conformational changes of proteins can be studied. There are multiple software and algorithms available for calculating the secondary structure components of proteins from CD spectrum data, such as CONTIN, SELCON, and CDSSTR, etc.