Structure-function studies of the C-terminal alpha-helix of human interleukin-2 by site-directed mutagenesis

By using oligonucleotide-mediated site-directed mutagenesis, we obtained three human interleukin-2 analogs with substitution of Pro in the C-terminal amphiphilic alpha-helix, 125Pro-IL-2, 127Pro-IL-2 and 125Pro-127Pro-IL-2. The bioactivities of all these analogs were decreased. The extent of the decrease in bioactivity coincided with the degrees of secondary and tertiary structure destroyed, as evaluated by circular dichroism and intrinsic fluorescence analysis. The results suggested that the integrity of the hydrophobic face in the C terminal alpha-helix is crucial for the structure and function of interleukin-2.