High-level secretion of human α₁-antitrypsin from Saccharomyces cerevisiae using inulinase signal sequence

Abstract

The use of a proper signal sequence is one of the major determinants for the efficient secretion of heterologous proteins from yeast. The signal sequence derived from inulinase (INU1A) of Kluyveromyces marxianus was evaluated in directing the secretion of a human glycoprotein, α1-antitrypsin (α1-AT), from Saccharomyces cerevisiae. A yeast expression vector for α1-AT was constructed by placing the coding sequence of human α1-AT fused with the INU1A. signal sequence downstream of the GAL10 promoter. S. cerevisiae transformants harboring the expression vector secreted about 70% of the total α1-AT synthesized into the culture media. The intracellularly retained form of α1-AT was mostly unglycosylated, whereas the secreted protein had high mannose-type glycosylation: The fed-batch cultivation of the recombinant yeast achieved a high-cell density, leading to the secretion of biologically active α1-AT up to 75 mg l-1. The secreted protein was purified and subjected to N-terminal sequencing, which confirmed that the secreted α1-AT was processed correctly at the Kex2 cleavage site as expected from the sequence of INU1A signal peptide. The results suggest that the inulinase signal sequence is useful for the high-level secretion of relatively large glycoproteins, such as human α1-AT, from S. cerevisiae.