Engineering split intein DnaE from Nostoc punctiforme for rapid protein purification
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We report the engineering of a DnaE intein able to catalyze rapid C-terminal cleavage in the absence of N-terminal cleavage. A single mutation in DnaE intein from Nostoc punctiforme PCC73102 (NpuDnaE), Asp118Gly, was introduced based on sequence alignment with a previously engineered C-terminal cleaving intein mini-MtuRecA. This mutation was able to both suppress N-terminal cleavage and significantly elevate C-terminal cleavage efficiency. Molecular modeling suggests that in NpuDnaE Asp118 forms a hydrogen bond with the penultimate Asn, preventing its spontaneous cyclization prior to N-terminal cleavage. Mutation of Asp118 to Gly essentially abolishes this restriction leading to subsequent C-terminal cleavage in the absence of N-terminal cleavage. The Gly118 NpuDnaE mutant exhibits rapid thio-dependent C-terminal cleavage kinetics with 80% completion within 3 h at room temperature. We used this newly engineered intein to develop both column-free and chromatography-based protein purification methods utilizing the elastin-like-polypeptide and chitin-binding protein as removable purification tags, respectively. We demonstrate rapid target protein purification to electrophoretic purity at yields up to 84 mg per liter of Escherichia coli culture.
author list (cited authors)
Ramirez, M., Valdes, N., Guan, D., & Chen, Z.