A positively charged protein domain, denoted Zbasic, can be used as a general purification tag for purification of recombinantly produced target proteins by cation-exchange chromatography. The Zbasic domain is constructed from the Protein A-derived Z-domain, and engineered to be highly charged, which allows selective capture on a cation exchanger at physiological pH values. Moreover, Zbasic is selective also under denaturing conditions and can be used for purification of proteins solubilized from inclusion bodies. Zbasic can then be used as a flexible linker to the cation-exchanger resin, and thereby allows solid-phase refolding of the target protein.Herein, protocols for purification of soluble Zbasic-tagged fusion proteins , as well as for integrated purification and solid-phase refolding of insoluble fusion proteins , are described. In addition, a procedure for enzymatic tag removal and recovery of native target protein is outlined.
Keywords: Fusion tag; Ion-exchange chromatography; Protein A; Proteolytic cleavage; Solid-phase refolding; Zbasic.