Application of circular dichroism spectroscopy in studying protein folding, stability, and interaction

Circular dichroism (CD) is a powerful spectroscopic technique used to study the changes in the structure and conformation of a protein. The wavelength ranges used for the structural assessment of protein are broadly classified into three regions. Far-UV CD (190–250 nm) is used to measure the secondary structure of proteins, which monitors any change in the peptide backbone. The near-UV CD (250–320 nm) monitors changes in the vicinity of aromatic amino acids in a protein, investigating the tertiary structure of proteins. Visible CD (350–700 nm) is used for monitoring the interaction of prosthetic groups (various metal ions) with proteins. Strong extrinsic CD bands of the extrinsic chromophore and intrinsic CD signals of protein can also be used to monitor protein–ligand interaction. Characteristic bands of aromatic residues (Trp, Tyr, and Phe) in the near-UV region can be used to examine the effect of mutations on the tertiary structure of proteins. This chapter presents an in-depth overview of CD spectroscopy’s basic principles, technical details, and applications.