Globular Protein Ultraviolet Circular Dichroic Spectra. Calculation from Crystal Structures via the Dipole Interaction Model

The dipole interaction model is used to calculate ultraviolet circular dichroic spectra of 16 globular proteins with various amounts of helix, sheet, and disordered regions. Structures for the calculations are based on crystal coordinates taken from the Brookhaven Protein Data Bank. Calculations for “reassembled fragment” models of the proteins reproduce the main features of observed solution CD spectra in the region of the amide π−π* transition near 200 nm. The predicted spectra for helix and sheet regions show considerable variation in magnitudes and wavelengths of the CD peaks, and a still wider variation is predicted for the disordered regions. A comparison of reassembled-molecule spectra with weighted averages of the spectra of the component fragments shows that deviations from additivity of the component spectra are generally small. The implications of these findings for attempts to resolve observed CD spectra in terms of a small number of components are discussed.