Involvement of the Fourth α-Helix of Mouse Granulocyte-Macrophage Colony-Stimulating Factor in Binding to the α-Subunit of the Receptor Complex

Abstract

Mouse granulocyte-macrophage colony-stimulating factor (mGM-CSF) proteins with substitutions for residues located within α-helix D were examined for biological activity and receptor binding properties. Alanine substitutions of the surface exposed positions indicated that several residues contribute to the ligand-receptor interface. Position K¹⁰⁸ and particularly D¹⁰² appeared to dominate the binding epitope recognized by mGM-Rα. Several amino acid substitutions were made for K¹⁰⁸ which reduced binding with concommitant losses in bioactivity. Substitutions for D¹⁰² resulted in binding affinities less than 0.1% that of the wild-type mGM-CSF and bioactivity decreased to 1.0%. Comparative analysis using high and low affinity binding conditions indicated that mGM-Rβ binding was unaffected by these mutations.

Key Words:

• GM-CSF
• receptor-ligand interactions
• structure-function
• mutagenesis