Abstract: Diabetes mellitus is a kind of serious endocrinopathy and insulin is the most effective medicine for the treatment of diabetes. The effective form of insulin when used as medicine is monomer. However,normal insulin usually forms polymers because of its high self-association,which makes it lag in the regulation of glucose level in blood. So it is necessary to develop monomeric insulin analogues. Research on the structure and function of insulin indicates that the interaction between the two insulin molecules of dimer insulin exists mainly between the two β-sheets of C terminus of B chains. There is a strong hydrophobic interaction between aromatic rings of B24,B25,B26 residues. The hydrophobic interaction is crucial for the formation of insulin dimer. B10 His residue is very important for the formation of hexamer. Based on these points,mutations were introduced to the interaction surface,expecting to get monomeric insulin with a low self-association. A mutant gene was constructed through asymmetric PCR. B10His residue was replaced with Glu and Asp was inserted between B24 and B25 residues. The gene was cloned into pBV220,which is a heat-inducing expression vector. The gene was expressed in E.Coli DH5α with a high level. Protein was purified through Sephacyl S-100 after denature and refolding. The proinsulin analogue was digested by trypsin and carboxypeptidase B,the product of which was purified through DEAE Sepharose and RP-HPLC. Protein identities were confirmed by MALDI-TOF mass spectrometry. Purified insulin analogue was obtained. The self-association of the insulin analogue was studied through analytical size exclusive chromatography with Superdex 75 column. The result showed an lower self-association than human insulin obviously. Conformation changes were studied through circular dichoism,results of which also showed the insulin analogue had a low self-association. These results indicated this insulin analogue had a strong monomeric property. B10His was replaced with Glu,and hexamer could not form. The acidic residue Asp was inserted between B24 and B25.It could destroy the hydrophobic interaction between molecules. These two factors could weaken the self-association of insulin greatly. The biological activity of the human insulin analogue was also studied in vitro. The relative activity of RIA was {73.7%}. The relative activity of RBA was 146%. The analogue retained high activities in vitro. It suggested that [B10Glu,B24-Asp-B25] human insulin could be a potential drug for the treatment of diabetes.

Key words: Insulin analogue, Monomeric insulin, Procaryotic expression, Biological activity