Cloning and heterologous expression of bovine pyroglutamyl peptidase type-1 in Escherichia coli: purification, biochemical and kinetic characterisation

We describe the cloning, expression and purification of the bovine XM866409 form of pyroglutamyl peptidase type-1 (PAP1). The cloned nucleotide sequence has an ORF coding for a primary sequence of 209 amino acid residues, which displays 98% identity with the human AJ278828 form of the enzyme. Three amino acid residues at positions 81, 205 and 208 were found to vary between the two sequences. The recombinant bovine PAP1 with a C-terminal His6 tag (rBtaPAP16H) was expressed in Escherichia coli XL10-Gold cells and purified by immobilised nickel ion affinity chromatography resulting in a yield of 2.6 mg of PAP1 per litre of culture. Purified rBtaPAP16H had a specific activity of 3633 units mg−1. SDS-PAGE revealed a band for bovine PAP1 with a molecular weight of ∼24 kDa, which is in good agreement with previously reported data on PAP1. The K m and k cat values obtained for rBtaPAP16H were 59 μM and 3.5 s−1, respectively. The optimum pH for activity was 9.0–9.5 and the optimum temperature was 37 °C. rBtaPAP16H was found to have an absolute requirement for the thiol-reducing agent DTT, consistent with the expected property of a cysteine protease. Kinetic studies using the peptides pGlu-His-Pro-NH2 (TRH), pGlu-Ala and pGlu-Val revealed K i values of 44.1, 141 and 652.17 μM, respectively. The lowest K i, observed for Thyrotropin-releasing Hormone (TRH), indicates that rBtaPAP16H has a higher affinity for tripeptides over dipeptides.