Single-chain insulin analogs as an insulin agonist and their implications for receptor binding

The importance of conformational change has recently become a focus for considering the mechanisms by which insulin and its receptor combine to achieve an effective ligand-receptor complex. Although the insulin structure bound to its receptor (active structure) is still unknown, there are evidences that conformational change takes place in the carboxy terminal region of the insulin B-chain on receptor binding. In the present study, we have produced various single-chain insulin analogs where C-terminus of B-chain and N-terminus of A-chain are connected by various short peptides. Significant increase of bioactivity was noticed when two pairs of dibasic residues were included as part of the connecting peptide, indicating that the distance between C-terminus of B-chain and N-terminus of A-chain changes due to the repulsive force between RR and KR residues, probably further apart than without the RR and KR residues. Protein modeling suggests that insulin and single-chain insulin analogs need to open up their receptor-binding pockets for their activities. The development of highly active single-chain insulin analog may facilitate the design of novel insulin analogs or non-peptide alternatives.