[11] Calculation of protein conformation from circular dichroism

This chapter discusses some recent developments in the estimation of various conformations in a protein molecule from its circular dichroism (CD) spectrum in the ultraviolet region. Optical rotatory dispersion (ORD) and CD are two chiroptical phenomena, which differentiate two enantiomers. They are caused by different interactions of left- and right-circularly polarized light with chiral molecules. Chirality is a geometric property of molecules; the corresponding substances are therefore optically active. At present CD has replaced ORD for the conformational analysis of proteins because CD bands that are characteristic of various secondary structures can be directly observed. The very simplicity of the CD method and the short time required for the measurements are extremely attractive. It is often advantageous to compare the CD analysis with empirical predictions of secondary structure of proteins from sequences, if such are available. All current methods for CD analysis are developed to determine not only the helix and β-form but also the β-turn and unordered forms.