Truncated thioredoxin peptides serves as an efficient fusion tag for production of proinsulin

: Several recombinant proteins of therapeutic value such as Proinsulin have long been produced from engineered E. coli strains. For the recombinant products to be produced at a commercially viable scale, selection of appropriate fusion tags would play a major role. Production of recombinant proteins with well-known fusion tags have posed problems associated with the high molecular weight, as these contribute to 50 - 80% of total expressed protein. The ratio of the recombinant protein to the fusion tags play a major role in enhancing the expression levels and determining the recovery percentage of small polypeptides such as proinsulin. Expressing proinsulin at a commercial scale needs fusion tags which will not only enhance the expression levels but also increase the protein stability. Furthermore, production of the heterologous recombinant protein in a soluble form will significantly avoid the cost involved in solubilizing inclusion bodies. Here we report that the usage of thioredoxin as a fusion tag helped enhancing the expression of proinsulin. To reduce the molar ratio of fusion tag TRX: Proinsulin, TRX tag was initially truncated into 6 fragments, and was further truncated into additional 5 tags ranging from 10 - 20 amino acids. Among the various truncated forms, FCTRX (1-15) sequence was selected as an ideal fusion tag. This tag can possibly be used as a fusion partner with any other recombinant proteins or peptides to be expressed in commercial scale.