title: Insight into the molecular basis for the kinetic differences between the two insulin receptor isoforms.
abstract: More than 20 years after the description of the two IR (insulin receptor) isoforms, designated IR-A (lacking exon 11) and IR-B (with exon 11), nearly every functional aspect of the alternative splicing both in vitro and in vivo remains controversial. In particular, there is no consensus on the precise ligand-binding properties of the isoforms. Increased affinity and dissociation kinetics have been reported for IR-A in comparison with IR-B, but the opposite results have also been reported. These are not trivial issues considering the reported possible increased mitogenic potency of IR-A, and the reported link between slower dissociation and increased mitogenesis. We have re-examined the ligand-binding properties of the two isoforms using a novel rigorous mathematical analysis based on the concept of a harmonic oscillator. We found that insulin has 1.5-fold higher apparent affinity towards IR-A and a 2-fold higher overall dissociation rate. Analysis based on the model showed increased association (3-fold) and dissociation (2-fold) rate constants for binding site 1 of IR in comparison with IR-B. We also provide a structural interpretation of these findings on the basis of the structure of the IR ectodomain and the proximity of the sequence encoded by exon 11 to the C-terminal peptide that is a critical trans-component of site 1.
authors.affiliation: Department of Insulin and Incretin Biology, Hagedorn Research Institute, Novo Nordisk A/S, Niels Steensens Vej 6, DK-2820 Gentofte, Denmark. lsek@novonordisk.com
authors.forename: Louise
authors.initials: L
authors.lastname: Knudsen
authors.forename: Pierre
authors.initials: P
authors.lastname: De Meyts
authors.forename: Vladislav V
authors.initials: VV
authors.lastname: Kiselyov
mesh_terms: D017398:Alternative Splicing; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D011972:Receptor, Insulin / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000819:agonists / Q000737:chemistry / Q000378:metabolism
chemical_list: D007328:Insulin; D007527:Isoenzymes; D011994:Recombinant Proteins; D011972:Receptor, Insulin