title: Role of the phenylalanine B24 side chain in directing insulin interaction with its receptor. Importance of main chain conformation.
abstract: We have investigated (by use of semisynthetic insulin analogs and isolated canine hepatocytes) the role of invariant residue PheB24 in determining the affinity of insulin-receptor interactions. Our results confirm that replacement of PheB24 by D-Phe is not detrimental to ligand binding to receptor, show that D-Ala is well tolerated at position B24 (whereas Ala is not), and demonstrate that [GlyB24]insulin retains as much as 78% of the receptor binding potency of native insulin. Additional findings show that replacement of PheB24 by D-Pro or by alpha-aminoisobutyric acid results in analogs with severely decreased binding potency, and that the COOH-terminal domain containing residues B26-B30 plays a positive role in determining receptor binding potency in GlyB24-substituted insulin (whereas it plays a negative role in determining the receptor binding potency of its GlyB25-substituted counterpart). We interpret our results as identifying (a) a critical role for the insulin main chain near residue B24 in determining the affinity of receptor for ligand, (b) the importance of main chain flexibility in achieving a high affinity state of receptor-bound hormone, and (c) a potential interaction of the PheB24 side chain with receptor which initiates main chain structural changes in the natural hormone, but which does not itself confer affinity to ligand-receptor interactions.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
authors.forename: R G
authors.initials: RG
authors.lastname: Mirmira
authors.forename: H S
authors.initials: HS
authors.lastname: Tager
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D066298:In Vitro Techniques; D007328:Insulin / Q000138:chemical synthesis / Q000502:physiology*; D008099:Liver / Q000378:metabolism; D010649:Phenylalanine; D011487:Protein Conformation; D011972:Receptor, Insulin / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D007328:Insulin; D010649:Phenylalanine; D011972:Receptor, Insulin