Expression and secretion of wheat germ agglutinin by Saccharomyces cerevisiae

Abstract

Genes encoding pre‐protein and prepro‐protein of wheat germ agglutinin isolectin 2 (WGA2) were chemically synthesized and expressed in the yeast Saccharomyces cerevisiae under the control of the ENO1 promoter. Yeast harboring either a pre‐WGA2 or a prepro‐WGA2 gene expression plasmid secreted a mature form of WGA2 into the culture medium. The amount of WGA2 secreted by the strain KS58‐2Ddel, which has a ssll mutation causing a supersecretion of human lysozyme [Suzuki, K., Ichikawa, K. & Jigami, Y. (1989) Mol. Gen. Genet. 219, 58–64], was 20‐fold greater than that secreted by the wild‐type strain KK4. The recombinant WGA2 from the cells containing the preproWGA2 gene expression plasmid was purified to homogeneity by a three‐step ion‐exchange chromatography scheme. As in wheat, the N‐terminal signal peptide of recombinant WGA2 purified from yeast culture was processed to form an N‐terminal 5‐oxoprolyl (pyroglutamyl) residue. Likewise, we found that the C‐terminal pro‐region of recombinant WGA2 had also been processed in yeast. Using electrospray ionization mass spectrometry, we found the processed C‐terminus to be heterogeneous in both recombinant WGA2 purified from yeast and in authentic WGA2. The major component of the recombinant WGA2 contained two additional amino acids at its C‐terminus compared to that of authentic WGA2. In spite of this difference in the C‐terminus, the recombinant WGA2 exhibited a sugar binding activity that was indistinguishable from that of authentic WGA2. Copyright © 1992, Wiley Blackwell. All rights reserved