A Lys27-to-Glu27 mutation in the human insulin-like growth factor-1 prevents disulfide linked dimerization and allows secretion of BiP when expressed in yeast.

Recombinant human insulin-like growth factor-1 (IGF1) secreted from yeast contains only 10-15% of the active monomer. A majority of the IGF1-like molecules are disulfide bonded dimers. These dimers are not formed in an IGF1 mutant where Lys27 has been replaced by glutamic acid. However, increased levels of secreted BiP (the yeast KAR2 gene product) are seen in cells expressing the mutant. These results imply that by preventing ionic interactions between two IGF1 molecules, intermolecular disulfide bonds do not form in yeast, and that in the mutant there is a structural change which induces BiP, allowing its secretion.