Yeast is a widely used recombinant protein expression system. We expanded its utility by engineering the yeast Pichia pastoris to secrete human glycoproteins with fully complex terminally sialylated N-glycans. After the knockout of four genes to eliminate yeast-specific glycosylation, we introduced 14 heterologous genes, allowing us to replicate the sequential steps of human glycosylation. The reported cell lines produce complex glycoproteins with greater than 90% terminal sialylation. Finally, to demonstrate the utility of these yeast strains, functional recombinant erythropoietin was produced.

We report the humanization of the glycosylation pathway in the yeast Pichia pastoris to secrete a human glycoprotein with uniform complex N-glycosylation. The process involved eliminating endogenous yeast glycosylation pathways, while properly localizing five active eukaryotic proteins, including mannosidases I and II, N-acetylglucosaminyl transferases I and II, and uridine 5'-diphosphate (UDP)-N-acetylglucosamine transporter. Targeted localization of the enzymes enabled the generation of a synthetic in vivo glycosylation pathway, which produced the complex human N-glycan N-acetylglucosamine2-mannose3-N-acetylglucosamine2 (GlcNAc2Man3GlcNAc2). The ability to generate human glycoproteins with homogeneous N-glycan structures in a fungal host is a step toward producing therapeutic glycoproteins and could become a tool for elucidating the structure-function relation of glycoproteins.

No abstract

Two autocrine proteins of 14 and 12 kilodaltons that induce the synthesis of rabbit fibroblast collagenase were identified. The proteins were purified from serum-free culture medium taken from rabbit synovial fibroblasts stimulated with phorbol myristate acetate. The amino-terminal sequences of the 14- and 12-kilodalton species were approximately 60 to 80 percent homologous with serum amyloid A and beta 2 microglobulin, respectively. The polyacrylamide gel-eluted proteins retained the ability to induce collagenase synthesis in rabbit and human fibroblasts. These autocrine proteins may provide a means to modulate collagenase synthesis in normal remodeling as well as in inflammation and disease states.