Synthesis and physicochemical characterization of major fragments of human leucocyte interferon alpha 1

Four oligopeptides corresponding to overlapping regions of the human leucocyte interferon alpha 1 (IFN) amino acid sequence have been synthesized by the solid-phase method. The physicochemical properties of these peptides were investigated by analytical ultracentrifugation and circular dichroism, absorbance, and fluorescence spectroscopies. IFNs 24-81 and 111-166 were shown to possess considerable ordered structure in solution. IFN 111-166 appeared to adopt a beta-stranded conformation, which could be reversibly unfolded by the addition of urea. Equimolar mixtures of IFNs 24-81 and 111-166 formed a noncovalent complex that was resistant to the formation of the Cys29-Cys139 disulfide bond found in native interferon alpha 1. Predictions of the secondary structure of interferon alpha 1 were made and the results compared to the measured properties of the fragments. In general, it was found that the prediction methods favored a highly alpha-helical conformation.