Dimeric Fragment of the Insulin Receptor α-Subunit Binds Insulin with Full Holoreceptor Affinity

摘要: The insulin receptor (IR) is a dimeric receptor, and its activation thought to involve cross-linking between monomers initiated by binding of single molecule separate epitopes on each monomer. We have previously shown that minimized consisting the first three domains human IR fused 16 amino acids from C-terminal alpha-subunit was monomeric bound with nanomolar affinity (Kristensen, C., Wiberg, F. Schaffer, L., Andersen, A. S. (1998) J. Biol. Chem. 273, 17780-17786). To investigate properties dimerized alpha-subunits, we reintroduced containing alpha-alpha disulfide bonds into this minireceptor. When inserting either fibronectin type III domain or full-length sequence exon 10, fragments were predominantly secreted as disulfide-linked dimers both had for insulin, similar found However, when these included obtained soluble 1000-fold higher (4-8 pm) what solubilized holoreceptor (14-24 pm). Moreover, dissociation labeled accelerated in presence unlabeled demonstrating another characteristic feature holoreceptor. This direct demonstration showing contains all required full affinity.