Fluorescence and site-directed mutagenesis studies of interleukin 1 beta

The authors mutated two key residues in the sequence of the cytokine interleukin 1 beta, namely the double mutant Phe46 to Trp46 and Trp120 to Phe120 and the single point mutation Lys103 to Leu103 and measured the resulting receptor binding and biological activities. The biological and receptor binding activities of the Trp46 mutein was reduced by a factor of 12 and 25, respectively, and surprisingly, those of the Leu103 mutein, 2600 and 600-fold relative to the wild-type protein. The authors had previously showed that Lys103 was unusually reactive to a variety of derivatizing agents. Furthermore, the Trp to Phe mutation allowed us to monitor the local environment of that residue by studying its intrinsic fluorescence properties, as well as any change in the fluorescence properties of Trp120 of the Leu103 mutein. The results of these studies show that mutation of Lys103 to Leu103 produces subtle long-range changes in the micro-environment of Trp120, indicative of a key role for this residue in the folding of the entire protein.