Recombinant protein purification by self-cleaving aggregation tag

A simple technique is presented for non- chromatographic purification of recombinant proteins expressed in Escherichia coli. This method is based on a reversibly precipitating, self-cleaving purification tag. The tag is made up of two components: an elastin- like polypeptide (ELP), which reversibly self-associates in high- salt buffers at temperatures above 30 degrees C; and an intein, which causes the ELP tag to self-cleave in response to a mild pH shift. Thus, a tripartite ELP-intein-target protein precursor can be purified by cycles of salt addition, heating and centrifugation. Once purified, intein-mediated self-cleavage, followed by precipitation of the cleaved ELP tag, allows easy and effective isolation of the pure, native target protein without the need for chromatographic separations. Recoveries of 50 - 100 mg of cleaved, native target protein per liter of shake-flask culture have been achieved for over a dozen proteins, typically in 8 - 24 h depending on specific process parameters.