ppiA also known as Peptidyl-prolyl cis-trans isomerase A. This is an enzyme found in both prokaryotes and eukaryotes that interconverts the cis and trans isomers of peptide bonds with the amino acid proline. Proline has an unusually conformationally restrained peptide bond due to its cyclic structure with its side chain bonded to its secondary amine nitrogen. Most amino acids have a strong energetic preference for the trans peptide bond conformation due to steric hindrance, but proline's unusual structure stabilizes the cis form so that both isomers are populated under biologically relevant conditions. Recombinant mouse ppiA, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.