Mini-proinsulins with a beta-turn motif

To increase the folding efficiency of proinsulin, we have designed a series of mini-proinsulins having the central C-peptide region replaced with sequences forming reverse turns. These proteins were produced as fusion proteins in E. coli in the form of inclusion bodies. After isolation process of the sulfonated mini-proinsulins, the subsequent refolding experiments indicate that the mini-proinsulins, with non-native penta-peptide sequences inserted between two of the enzyme processing sites, show substantially increased folding yields compared with the proinsulin. The correct disulfide connections were verified by fingerprint analysis using Glu-C endoproteinase. These novel mini-proinsulins could be used for the study of folding mechanism of proinsulin.