A cleavable self-assembling tag strategy for preparing proteins and peptides with an authentic N-terminus

Recombinant protein expression and purification remains a central need for biotechnology. Herein, the authors report a streamlined protein and peptide purification strategy using short self-assembling peptides and a C-terminal cleavage intein. In this strategy, the fusion protein is first expressed as an aggregate induced by the self-assembling peptide. Upon simple separation, the target protein or peptide with an authentic N-terminus is then released in the solution by intein-mediated cleavage. Different combinations of four self-assembling peptides (ELK16, L₆ KD, FK and FR) with three inteins (Sce VMA, Mtu ΔI-CM and Ssp DnaB) were explored. One protein and two peptides were used as model polypeptides to test the strategy. The intein Mtu ΔI-CM, which has pH-shift inducible cleavage, was found to work well with three self-assembling peptides (L₆ KD, FR, FK). Using this intein gave a yield of protein or peptide comparable with that from other more established strategies, such as the Trx-strategy, but in a simpler and more economical way. This strategy provides a simple and efficient method by which to prepare proteins and peptides with an authentic N-terminus, which is especially effective for peptides of 30-100 amino acids in length that are typically unstable and susceptible to degradation in Escherichia coli.