Calculation and use of protein‐derived conformation‐related spectra for the estimate of the secondary structure of proteins from their infrared spectra

Abstract

Abstract This paper probes the calculation of conformation‐related basis spectra from infrared spectra (amide I′band) of reference proteins of known conformational composition and, with their aid, the computation of conformations from the amide I′ band of globular proteins using in both approaches a least‐squares, curve‐fitting computer program for the analysis of the spectra. The following results were obtained. The infrared basis spectra for the α‐helix conformation, the β‐(antiparallel‐chain pleated sheet) conformation and the ρ‐conformation were calculated and their physical reality was substantiated. The basis spectra were shown to be similar when the absorption contributions of the side chains of amino acids were either neglected or taken into account (uncorrected or corrected basis spectra). The mutual correlation of the basis spectra, quantified by the roots of the diagonal elements of the inverse matrix, was found to be low enough only for the β‐conformation to allow a statistically reliable estimate of the β‐conformation content of proteins. The comparison of the percentages of the β‐conformation derived from x‐ray structural analysis or calculated from infrared spectra showed the suitability of the basis spectra for the rough estimate of the β‐conformation percentages of proteins. The results were not significantly different when using the uncorrected or corrected basis spectra.