Glycosylation of human alpha 1-antitrypsin in Saccharomyces cerevisiae and methylotrophic yeasts.

Human alpha 1-antitrypsin (alpha 1-AT) is a major serine protease inhibitor in plasma, secreted as a glycoprotein with a complex type of carbohydrate at three asparagine residues. To study glycosylation of heterologous proteins in yeast, we investigated the glycosylation pattern of the human alpha 1-AT secreted in the baker's yeast Saccharomyces cerevisiae and in the methylotrophic yeasts, Hansenula polymorpha and Pichia pastoris. The partial digestion of the recombinant alpha 1-AT with endoglycosidase H and the expression in the mnn9 deletion mutant of S. cerevisiae showed that the recombinant alpha 1-AT secreted in S. cerevisiae was heterogeneous, consisting of molecules containing core carbohydrates on either two or all three asparagine residues. Besides the core carbohydrates, variable numbers of mannose outer chains were also added to some of the secreted alpha 1-AT. The human alpha 1-AT secreted in both methylotrophic yeasts was also heterogeneous and hypermannosylated as observed in S. cerevisiae, although the overall length of mannose outer chains of alpha 1-AT in the methylotrophic yeasts appeared to be relatively shorter than those of alpha 1-AT in S. cerevisiae. The alpha 1-AT secreted from both methylotrophic yeasts retained its biological activity as an elastase inhibitor comparable to that of alpha 1-AT from S. cerevisiae, suggesting that the different glycosylation profile does not affect the in vitro activity of the protein.