Purification and characterization of the recombinant human prostaglandin H synthase-2 expressed in Pichia pastoris

Enhanced expression of human prostaglandin H synthase-2 in the yeast Pichia pastoris and removal of the C-terminal tag with bovine carboxypeptidase A

Vertebrate prostaglandin H synthases (PGHSs) are membrane-bound disulphide-containing hemoglycoproteins. Therefore, eukaryotic expression systems are required for the production of recombinant PGHSs. Recently we announced the expression of human PGHS-2 (hPGHS-2) in the yeast Pichia pastoris. Here we report improved production of hPGHS-2 in P. pastoris and a convenient method for the purification and de-tagging of the protein. An affinity tag comprised of a proline, a glycine and eight histidines was introduced into the C-terminal end of hPGHS-2. The tagged hPGHS-2 was expressed intracellularly in P. pastoris under the control of a constitutive or methanol-inducible promoter. Compared to constitutive expression, methanol-induced expression yielded approximately four times more protein. The analysis of high and low gene copy number recombinants revealed a positive correlation between the gene copy number and the expression level of hPGHS-2. The recombinant hPGHS-2 was purified using immobilised metal ion affinity chromatography. A novel elution method, treatment of the affinity resin with bovine carboxypeptidase A, was employed. The yield of pure de-tagged hPGHS-2 from 1l of yeast culture was approximately 3mg. The protein purification process with simultaneous removal of the C-terminal polyhistidine tag could be easily applied for the affinity purification of other proteins.

N-glycosylation site occupancy in human prostaglandin H synthases expressed in Pichia pastoris

Prostaglandin H synthases (PGHSs) are N-glycosylated membrane proteins that catalyse the committed step in prostaglandin synthesis. Unlike PGHS-2, the production of recombinant PGHS-1 in non-mammalian expression systems is complicated. The majority of the heterologous enzyme is inactive due to misfolding. Correct N-glycosylation is proposed to be obligatory for proper folding of mammalian PGHSs. In this study, human PGHS-1 and -2 (hPGHS-1 and -2) were expressed in the yeast Pichia pastoris. Recombinant hPGHS-2 was catalytically active, whereas hPGHS-1 was inactive. Accumulation of non-glycosylated hPGHSs was not observed in the crude lysate of the yeast cells. The N-glycosylation patterns of the purified recombinant proteins were characterised using nano-LC/MS/MS. The isoforms exhibited similar N-glycosylation site occupancy. The results indicate that there are more complex grounds for the inactivity of the recombinant hPGHS-1 produced in yeast.