Basal autophosphorylation of insulin receptor occurs preferentially on the receptor conformation exhibiting high affinity for insulin and stabilizes this conformation.
Insulin signal transmission through the plasma membrane was studied in terms of relationship between basal autophosphorylation of the beta-subunit and the ability to bind insulin by the alpha-subunit of the insulin receptor. In a cell free system, receptors phosphorylated on tyrosine residues in the absence of insulin were separated from non-phosphorylated receptors using antiphosphotyrosine antibodies. Insulin binding assays were then performed on basally autophosphorylated and on non-phosphorylated receptors. We found that the tyrosine phosphorylated receptors, which corresponded to 25% of the total number of receptors, were accountable for 60-80% of insulin binding. Scatchard representation of binding data has shown that the plot corresponding to tyrosine phosphorylated receptors was localized above, and was steeper than the plot corresponding to non-phosphorylated receptors. These data make it likely that the conformation of alpha-subunit which favours ligand binding is connected to the conformation of beta-subunit which favours phosphate reception on tyrosine residues. Reciprocally, the high-affinity conformation of insulin receptor seems to become stabilized by basal autophosphorylation.
Kubar
J
J
Institut National de la Santé et de la Recherche Médicale INSERM U145. Faculté de Médecine, Nice, France.
Rochet
N
N
D000818:Animals; D002460:Cell Line; D007328:Insulin / Q000378:metabolism*; D007700:Kinetics; D010766:Phosphorylation; D011487:Protein Conformation; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism
D007328:Insulin; D014443:Tyrosine; D011972:Receptor, Insulin