Production of human α₁ proteinase inhibitor from Aspergillus niger

Background

α₁ proteinase inhibitor (α₁PI) belongs to the serin protease inhibitor (serpin) family; it is responsible for 90% of the trypsin inhibitory capacity of human plasma. Its primary physiological role is to inhibit neutrophil elastase that degrades elastin, collagen and proteoglycan and can cause extensive lung damage. α₁PI deficiency can result in lung emphisema in adults, liver disease in children and is also associated with cystic fibrosis, arthritis and other malignant conditions [1–3]. Human plasma-derived α₁PI is a licensed product used for replacement therapy. Although viral inactivation measures are taken, products derived from human plasma carry the risk of contamination with blood-borne pathogens, and therefore recombinant is an attractive alternative.

α₁PI exhibits a molecular mass of approximately 52 kD, has 394 amino acids, a single cystein residue and three carbohydrate attachment sites at asparagine residues 46, 83 and 247 [4, 5]. Significant research effort was directed to produce recombinant human α₁PI in E. coli [6], yeast [7], transgenic mice and sheep as well as plant cells [3]. E-coli produced an unglycosylated product, the yeast produced incorrect glycosylation and the transgenic animals pose the same threats as plasma derived product.

Results

Human α₁PI was cloned and expressed in Aspergillus niger, filamentous fungus that can grow in defined media and had the ability to perform glycosylation. Submerged culture conditions were established: using starch as carbon source, 30% dissolved oxygen concentration, pH 7.0 and 28°C; 10 mg per liter of active α₁PI were secreted to the growth media in 40 hours. Controlling the protein proteolysis was found to be an important factor in the production from the fungus. The effect of carbon sources and growth conditions on the production and stability of the protein will be presented and evaluated.