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Pichia pastoris is an important host for recombinant protein production. As a protein production platform, further development for therapeutic glycoproteins has been hindered by the high-mannose-type N-glycosylation common to yeast and fungi. Such N-glycans can complicate downstream processing, might be immunogenic or cause the rapid clearance of the glycoprotein from circulation. In recent years, much effort has gone to engineering the N-glycosylation pathway of Pichia pastoris to mimic the human N-glycosylation pathway. This can be of pivotal importance to generate the appropriate glycoforms of therapeutically relevant glycoproteins or to gain a better understanding of structure-function relationships.This chapter describes the methodology to create such glyco-engineered Pichia pastoris strains using the GlycoSwitch(®). This strategy consists of the disruption of an endogenous glycosyltransferase and the heterologous expression of a glycosidase or glycosyltransferase targeted to the Endoplasmic Reticulum or the Golgi of the host. For each step in the process, we describe the transformation procedure, small-scale screening and we also describe how to perform DNA-Sequencer-Aided Fluorophore-Assisted Capillary Electrophoresis (DSA-FACE) to select for clones with the appropriate N-glycosylation profile. The steps described in this chapter can be followed in an iterative fashion in order to generate clones of Pichia pastoris expressing heterologous proteins with humanized N-glycans.

Serum protein electrophoresis is widely used in clinical laboratories to measure the relative abundance of each obtained fraction. Moreover, we found that the migration time of the γ-globulin fraction can be reproducibly determined (CV = 1.1%). Immunoglobulins were purified from serum using protein L-agarose and their N-glycosylation was studied using CE on a DNA sequencer. Liver fibrosis patients showed a lower level of sialylation and this moderately correlates with the migration time of the γ-globulins (r = 0.2-0.4). This allowed us to differentiate healthy individuals from these patients with an acceptable diagnostic accuracy (area under the curve = 0.75). This glycomics approach could become a significant added value to a daily, routine clinical test.

Glycosylation research has gained significant attention in several research fields including immunology, protein production, and biomarker discovery. However, complex and time-consuming protocols are often necessary to obtain suitable samples for analysis. We here describe a short and robust assay to prepare 8-aminopyrene-1,3,6-trisulphonic acid-labeled N-glycans from serum samples. It only involves the subsequent addition of reagents and incubation in a PCR thermocycler. Moreover, this assay allows the detection of these glycans, which are only present in minute amounts in serum, on high-throughput microfluidics CE platforms including the MCE-202 MultiNA, 2100 Bioanalyzer, and eGene system. Using this clinical glycomics assay, we could reliably measure GlycoHepatoTest, a panel of biomarkers allowing the follow-up of chronic liver disease patients from the early stage onward.

Yeast surface display is being employed as an efficient tool for the isolation and engineering of traditional antibody fragments, both scFv and Fab, as well as single domain antibodies. Here we describe the protocols for a yeast surface display system developed in the methylothrophic yeast Pichia pastoris, the most commonly used yeast species for protein production. In this system the immune or maturated library of single domain antibodies is fused to the C-terminal domain of Saccharomyces cerevisiae alpha-agglutinin gene (SAG1) and expressed on the surface of P. pastoris cells. Labeling with ligands enables rapid and quantitative analysis in conjunction with isolation of single domain antibodies with the desired characteristics.

Glycosylation is an important issue in heterologous protein production for therapeutic applications. Glycoproteins produced in Pichia pastoris contain high mannose glycan structures that can hamper downstream processing, might be immunogenic, and cause rapid clearance from the circulation. This chapter describes a method that helps solving these glycosylation-related problems by inactivation of OCH1, overexpression of an HDEL-tagged mannosidase, and overexpression of a Kre2/GlcNAc-transferase I chimeric enzyme. Different plasmids are described as well as glycan analysis methods.