Affinity conversion of receptors for colony stimulating factors: properties of solubilized receptors.
Murine receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and Multi-CSF (interleukin-3) can exist in both high- and low-affinity forms and demonstrate trans-modulation by several different ligands. In contrast the recently cloned human GM-CSF receptor and murine interleukin-3 (IL-3) receptor display only low-affinity binding. To begin to understand the molecular basis of the formation of high- and low-affinity receptors and their trans-modulation we have developed methods for the solubilization and assay of GM-CSF and interleukin-3 receptors so that their binding characteristics can be studied in cell-free solution. Both receptors displayed a single class of high-affinity binding on intact FDC-P1 cells and IL-3 receptors had unaltered binding characteristics in cells, membranes and in detergent solution. However, GM-CSF receptors were converted to a single class of low-affinity binding in detergent solution while both high- and low-affinity forms were evident in membranes. The basis of affinity conversion of GM-CSF receptors was exclusively a change in the kinetic dissociation rate of ligand. Cross-linking experiments suggested that high-affinity receptors for GM-CSF and IL-3 might consist of two different protein species and, if this is so, the data suggest that this association is more stable for IL-3 than for GM-CSF receptors.
Nicola
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Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria, Australia.
Cary
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D000818:Animals; D001854:Bone Marrow Cells; D002460:Cell Line; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents; D003902:Detergents; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D009994:Osmolar Concentration; D011485:Protein Binding; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D016185:Receptors, Interleukin-3 / Q000378:metabolism*; D012995:Solubility; D013329:Structure-Activity Relationship
D003432:Cross-Linking Reagents; D003902:Detergents; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D016185:Receptors, Interleukin-3