The protein SlyD from Escherichia coli is a peptidyl prolyl cis-trans isomerase (PPI), and therefore a useful protein reagent for in vitro folding reactions. Its sequence contains a stretch of five histidine residues, interrupted by a non-histidine residue (HHHxHH) much like a 6xHis residue hexahistidine affinity tag. We show in this paper that, in the absence of any other 6xHis tag-bearing recombinant protein, SlyD is most efficiently purified from E. coli through standard Nickel-nitrilotriacetic acid (Ni-NTA) based imidazole metal affinity chromatography (IMAC).

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