Computation and analysis of protein circular dichroism spectra.

Introduction Circular dichroism (CD) is the most widely used form of chiroptical spectroscopy, spectroscopic techniques that utilize the differential interaction of molecules with left− and right−circularly polarized light. In the absence of a magnetic field, the molecule must be chiral to give rise to a difference in the interaction with the two types of circularly polarized light. The phenomenon of CD consists of the differential absorption of left− and right−circularly polarized light by a chiral molecule. Circular dichroism due to electronic transitions is generally referred to as CD (also as ECD), and that due to vibrational transitions as VCD. There are other types of chiroptical spectroscopy, which include circularly polarized luminescence, circular intensity differential scattering, and Raman optical activity. In this chapter we discuss the origins of electronic CD in proteins, theoretical methods for computing protein CD, and empirical analysis of CD for estimating structural composition of proteins. A large number of scientists have contributed to our understanding of protein CD. Given the wide scope of this chapter and space limitations, we have been forced to be highly selective in our references, citing representative papers and review articles.