Expression and Purification of Native Human Granulocyte-Macrophage Colony-Stimulating Factor from an Escherichia coli Secretion Vector

The human granulocyte-macrophage colony stimulating factor (GM-CSF) was expressed and purified from a high-level Escherichia coli secretion vector. A cDNA fragment encoding mature GM-CSF was fused with the aid of a synthetic oligonucleotide to the E. coli outer membrane signal peptide (ompA) of the secretion expression vector pIN-III-ompA3. The primary construction, designated pLB5001, is under transcriptional control of the tandem lipoprotein promoter (lpp ^P) lactose promoter-operator (lac ^PO), and is regulated by the lactose repressor. Upon induction, a polypeptide of MW = 14,600 was produced which had GM-CSF activity in a human bone marrow colony assay. The linker sequence between the ompA signal peptide and the amino terminus of the mature GM-CSF was removed by oligonucleotide-directed site-specific mutagenesis to produce GM-CSF with an authentic amino terminus. The resulting construct, designated pLB5001-4, expressed authentic GM-CSF with a specific activity similar to that observed for the pLB5001 specified GM-CSF. Both versions of GM-CSF were associated with the membrane fraction after osmotic shock, and were purified to homogeneity by DEAE-Sephacel chromatography, followed by reversed-phase HPLC. Amino acid sequencing from the amino terminus of the purified GM-CSF established that the ompA signal peptide was cleaved at its normal processing site in both cases.