Importance of main-chain flexibility and the insulin fold in insulin-receptor interactions.

We have investigated the effects of altering the disposition between the COOH-terminal B chain domain of insulin and the core of the insulin molecule on ligand interactions with the hepatocyte insulin receptor. Analogues include those in which ArgB22 of des-octapeptide(B23-B30)-insulin is extended by one to three residues of glycine prior to termination in Phe-NH2, by one to five residues of glycine prior to termination in Phe-Phe-NH2, or by an additional residue of glycine prior to termination in more extended sequences derived from insulin or [GlyB24]insulin. Analogues were also examined with respect to their abilities to form hexamers in solution in the presence of Co2+, phenol, and NaSCN. Overall, our studies of ligand-receptor interactions identify that (a) the energetic penalty for the introduction of a single residue of glycine is uniform in all classes of analogues for up to three residues of glycine but diminishes somewhat for analogues with longer insertions and (b) the COOH-terminal residues of the B chain retain their importance for all classes of analogues, no matter the number of glycine residues introduced. Analogues with glycine insertions, but not those with glycine substitutions, readily form thiocyanate-stabilized complexes with Co2+ in the presence of phenol.(ABSTRACT TRUNCATED AT 250 WORDS)