The ligand binding characteristics of a kinase-defective A/K1018 human insulin receptor expressed in Rat 1 fibroblasts.
Expression of the cDNA encoding a human insulin receptor with replacement of alanine for lysine at residue 1018 in the ATP binding domain of the beta subunit results in a receptor that is not only kinase-defective, but also biologically inactive. Interestingly, this mutated receptor shows a decreased insulin binding affinity when expressed at high level. We, therefore, studied the binding property of this mutant receptor expressed in Rat 1 fibroblasts. The association rate (Ka) of insulin to the mutant receptor was comparable to normal, but the dissociation rate (Kd) was twice as fast. Furthermore, the Kd of the mutant receptor was also more sensitive to changes in pH, accelerating more rapidly with pH changes than did the Kd of normal receptors. Despite this difference, the mutant receptor still exhibited negative cooperativity. These results indicate that the loss of tyrosine kinase activity of the beta subunit of the insulin receptor leads to alteration of the ligand binding affinity of the alpha subunit.
Third Department of Medicine, Shiga University of Medical Science, Japan.
H
H
Maegawa
M
M
Kobayashi
K
K
Egawa
D A
DA
McClain
J M
JM
Olefsky
Y
Y
Shigeta
D000818:Animals; D002460:Cell Line; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D009154:Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*
D007328:Insulin; D008024:Ligands; D011494:Protein Kinases; D011972:Receptor, Insulin