Effect of location of the His-tag on the production of soluble and functional Buthus martensii Karsch insect toxin

The low yield and poor folding efficiency in vivo of soluble and active recombinant cysteine-rich proteins expressed in Escherichia coli are a major challenge for large-scale protein production and purification. Expression vectors containing Buthus martensii Karsch insect toxin (BmK IT) fused to the C terminus of the intein Ssp DnaB were constructed in an attempt to overcome this problem. Following purification and intein self-cleavage, the fusion protein His6-intein-IT produced insoluble BmK IT, while intein-IT-His6 generated soluble and properly folded BmK IT. This result indicated that the positioning of the His6 tag has a key role in the production of soluble and functional BmK IT.