Purification of a Tat leader peptide by co-expression with its chaperone

We present a method for the purification of the 45 residue long leader peptide of Escherichia coli dimethyl sulfoxide reductase subunit A (DmsAL), a substrate of the twin arginine translocase, by co-expressing the leader peptide with its specific chaperone protein, DmsD. The peptide can be isolated from the soluble DmsAL/DmsD complex or conveniently from the lysate pellet fraction. The recombinant leader peptide is functionally intact as the peptide/chaperone complex can be reconstituted from purified DmsAL and DmsD. A construct with DmsAL fused to the N-terminus of DmsD (DmsAL–DmsD fusion) was created to further explore the properties of the leader peptide-chaperone interactions. Analytical size-exclusion chromatography in-line with multi-angle light scattering reveals that the DmsAL–DmsD fusion construct forms a dimer wherein each protomer binds the neighboring leader peptide. A model of this homodimeric interaction is presented.