Expression, purification and characterization of recombinant murine granulocyte-macrophage colony-stimulating factor...

Expression and secretion of two lymphokines, murine granulocyte-macrophage colony-stimulating factor (MuGM-CSF) and bovine interleukin-2 (BoIL-2), to levels of 50-60 mg per liter were achieved by placing these cDNAs in a Saccharomyces cerevisiae expression vector that utilized the yeast alcohol dehydrogenase-2 promoter and alpha-factor leader peptide. These lymphokines were purified to homogeneity by direct application of the crude yeast medium to reversed-phase high-performance liquid chromatography. Despite the fact that both lymphokines contain at least one N-glycosylation site and have identical N-terminal residues (Ala-Pro-Thr), recombinant (R) GM-CSF was found to be heterogeneously glycosylated by yeast while RBoIL-2 was secreted without glycosylation. Additionally, approximately 40% of the RGM-CSF was found to be proteolytically cleaved after the second amino acid residue, while RBoIL-2 was found to be intact.