Fig. 1

The icSAT scheme for the purification of target proteins. a Schematic diagram of the icSAT scheme. The sequences of three salt-inducible self-assembling peptides (CpA, IpA and MpA) are shown in Fig. 1a, with hydrophobic residues highlighted in blue for clarity. The proposed icSAT tag is composed of one of the three peptides (CpA, IpA or MpA), a linker (i.e., PT linker [24]), and an intein (i.e., Mtu ΔI-CM). When the salt concentration is increased to a suitable level, the icSAT tag induces the fusion protein to form an insoluble aggregate that can be conveniently harvested by centrifugation. Subsequent treatment of the harvested aggregate with intein-mediated cleavage releases the target protein into solution. b-d Purification of hGH from the fusion protein MpA-Mtu ΔI-CM-hGH with three high-salt conditions. EP: precipitate of the cell lysate after expression, ES: supernatant of the cell lysate after expression, ESS: supernatant of salt-induced aggregation, ESP: precipitate of salt-induced aggregation, CP: precipitate of intein-mediated cleavage, CS: supernatant of intein-mediated cleavage, M1: protein marker. (b) 0.7 M Na₂SO₄, (c) 3 M NaCl, (d) 0.7 M (NH₄)₂SO₄