31] Circular dichroism for determining secondary structure and state of aggregation of membrane proteins

Abstract

Publisher Summary The determination of the secondary structure of water-soluble proteins by means of far-UV circular dichroism (CD) spectra is a widely used method. These spectra, in the range from 185 to 240 nm, are mainly because of the identical peptide group chromophores of the protein backbone and are quite sensitive to the backbone conformation. The coefficients directly provide the percentages of the various secondary structures present. Chromophore–chromophore interactions are well known in the absorption and CD spectra of proteins and nucleic acids. When the identical peptide chromophores of the protein backbone are regularly arranged, such as in an α-helix, exciton-coupling effects are observed in the far-UV that are particularly evident in the CD spectra, and they are used for the secondary structure determination. When the nearly identical nucleic acid bases stack in the regular structure of a double helix, pronounced exciton-coupling effects are observed in the CD spectra, which depend on the detailed stacking geometry and on the helix sense.