We have investigated (by use of semisynthetic insulin analogs and isolated canine hepatocytes) the role of invariant residue Phe(B24) in determining the affinity of insulin-receptor interactions. Our results confirm that replacement of Phe(B24) 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 [Gly(B24)]insulin retains as much as 78% of the receptor binding potency of native insulin. Additional findings show that replacement of Phe(B24) by D-Pro or by α-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 Gly(B24)-substituted insulin (whereas it plays a negative role in determining the receptor binding potency of its Gly(B25)-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 Phe(B24) 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.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - Jan 1 1989|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology