Role of polycationic C-terminal portion in the structure and activity of recombinant human interferon-gamma

Purified recombinant human interferon-gamma, produced in Escherichia coli, was digested with trypsin under mild conditions, resulting in a preparation containing approximately 90% of a Mr = 15,800 protein and 10% of a 14,400 protein. The Mr = 15,800 protein has an intact N terminus and the Mr = 14,400 protein lacks 14 N-terminal residues. Both proteins lack C terminus of approximately 13 residues. This preparation containing the Mr = 15,800 and 14,400 proteins was identical with the intact protein with respect to conformation and dimerization, as analyzed by circular dichroism and gel filtration. However, the antiviral activity of this preparation was 1000-fold lower than that of the intact molecule. Since the majority of this preparation is the Mr = 15,800 protein, these results suggest that the C terminus does not affect the protein conformation and self-association, but greatly alters antiviral activity.