COMPUTED CIRCULAR DICHROISM SPECTRA FOR EVALUATION OF PROTEIN CONFORMATION

Circular dichroism curves of poly-L-lysine containing varying amounts of α helix, β-pleated sheet, and random coil segments have been computed in the 190-250-mμ region. The application of these curves for determining protein conformation is discussed. The circular dichroism curves of several proteins, whose three-dimensional structures are known from X-ray diffraction studies, have been fitted by a linear combination of the three reference structures in the 208-240-mμ region. The results show that these computed curves are very useful in predicting protein structure, and if the protein possesses a high degree of secondary structure, the agreement between the calculated and the X-ray diffraction determined structure is extremely good. If the protein is largely nonregular, the results are less satisfactory but are still informative. The results show that the use of circular dichroism is a decided improvement over the use of optical rotatory dispersion for the evaluation of protein conformation. © 1969, American Chemical Society. All rights reserved.