A new pH-responsive peptide tag for protein purification

This paper describes a new pH-responsive peptide tag that adds a protein reversible precipitation and redissolution character. This peptide tag is a part of a cell surface protein B (CspB) derived from Corynebacterium glutamicum. Proinsulin that genetically fused with a peptide of N-terminal 6, 17, 50, or 250 amino acid residues of CspB showed that the reversible precipitation and redissolution depended on the pH. The transition occurred within a physiological and narrow pH range. A CspB50 tag comprising 50 amino acid residues of N-terminal CspB was further evaluated as a representative using other pharmaceutical proteins. Below pH 6.8, almost all CspB50-Teriparatide fusion formed an aggregated state. Subsequent addition of alkali turned the cloudy protein solution transparent above pH 7.3, in which almost all the CspB50-Teriparatide fusion redissolved. The CspB50-Bivalirudin fusion showed a similar behavior with slightly different pH range. This tag is offering a new protein purification method based on liquid-solid separation which does not require an affinity ligand. This sharp response around neutral pH is useful as a pH-responsive tag for the purification of unstable proteins at a non-physiological pH.