Contribution of the absolutely conserved B8Gly to the foldability of insulin.

B8Gly is absolutely conserved in insulin from different species, and in other members of the insulin superfamily the corresponding position is always occupied by a Gly residue. However, the reasons for its conservation are still unclear; probably many factors contribute to this phenomenon. In our previous work, B8Gly was replaced by an Ala residue, which suggested that biological activity is one of the factors contributing to its conservation. In order to identify more factors contributing to this positional conservation, the secretion efficiency, structural stability, disulfide stability, and in vitro refolding of single-chain insulin (PIP) and a mutant with B8Gly replaced by Ala, were investigated. Compared with wild-type PIP, the B8Ala replacement decreased the secretion efficiency, structural stability, disulfide stability, and in vitro refolding efficiency of the PIP sequence. These results suggest that B8Gly is important to the secretion, folding, and stability of the insulin sequence.