ANTIBODIES TO THE EXTRACELLULAR RECEPTOR DOMAIN RESTORE THE HORMONE-INSENSITIVE KINASE AND CONFORMATION OF THE MUTANT INSULIN-RECEPTOR VALINE-382

A mutation substituting a valine for phenylalanine at residue 382 in t he insulin receptor alpha-subunit has been found in two sisters with a genetic form of extreme insulin resistance. This receptor mutation im pairs the ability of the hormone to activate autophosphorylation of so lubilized receptors and phosphorylation of substrates (Accili, D., Mos thaf, L., Ullrich, A., and Taylor, S. I. (1991) J. Biol. Chem. 266, 43 4-439). We have previously demonstrated that in native receptors insul in induces a conformational change in the receptor beta-subunit, which is thought to be necessary for receptor activation (Baron, V., Gautie r, N., Komoriya, A., Hainaut, P., Scimeca, J. C., Mervic, M., Lavielle , S., Dolais-Kitabgi, J., and Van Obberghen, E. (1990) Biochemistry 29 , 4634-4641). Hence, it was thought that a defect in this conformation al change might explain the functional defect of the mutant receptor. This appears to be the case, as we demonstrate here that the mutant re ceptor is locked in its inactive configuration. However, we found two monoclonal antibodies, directed to the extracellular domain, which are capable of restoring the mutant receptor kinase activity. The activat ion of the mutant receptor was accompanied by restoration of conformat ional changes in the beta-subunit C terminus. From these data, we draw the two following conclusions. (i) A causal link exists between recep tor kinase activation and the occurrence of conformational changes. (i i) Ligands other than insulin, such as antibodies, which perturb the e xtracellular domain, can function as alternative ways to restore the m utant receptor kinase.