Deletion Mutants of Human Granulocyte-Macrophage Colony-Stimulating Factor

To study the structure–function relationship of the human granulocyte-macrophage colony-stimulating factor (GM-CSF), genes were constructed that encode its three deletion mutants: D1, a mutant with the deletion of six amino acid residues (37–42) some of which are a part of a -structural region; D2, a mutant with the deletion of the unstructured six-aa sequence of a loop (45–50); and D3, a mutant with the deletion of 14 aa residues (37–50) corresponding to the A–B loop and encoded by the second exon of the gmcsf gene. The expression products of these genes in E. coli were accumulated in a fraction of insoluble proteins. The secondary structures of the mutant proteins were similar to that of the full-size GM-CSF, but the biological activity of the deletion mutants was 130 times lower than that of the GM-CSF: they stimulated the proliferation of the TF-1 cell line at 3 ng/ml concentration. The resulting proteins displayed antagonistic properties toward the full-size GM-CSF, with the inhibition degree of its colony-stimulating activity being 27%. A decrease in the mutant activity in the row D2 > D1 > D3 implies the importance of the conserved hydrophobic residues involved in the formation of the -structure for the formation of the GM-CSF functional conformation.