Mining Data From Plasma Cell Differentiation Identified Novel Genes for Engineering of a Yeast Antibody Factory

Modification of the endoplasmic reticulum morphology enables improved recombinant antibody expression in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is a versatile cell factory used for manufacturing of a wide range of products, among them recombinant proteins. Protein folding is one of the rate-limiting processes and this shortcoming is often overcome by the expression of folding catalysts and chaperones in the endoplasmic reticulum (ER). In this work, we aimed to establish the impact of ER structure on cellular productivity. The reticulon proteins Rtn1p and Rtn2p, and Yop1p are membrane curvature inducing proteins that define the morphology of the ER and depletion of these proteins creates yeast cells with a higher ER sheet-to-tubule ratio. We created yeast strains with different combinations of deletions of Rtn1p, Rtn2p, and Yop1p coding genes in cells with a normal or expanded ER lumen. We identified strains that reached up to 2.2-fold higher antibody titres compared to the control strain. The expanded ER membrane reached by deletion of the lipid biosynthesis repressor OPI1 was essential for the increased productivity. The improved specific productivity was accompanied by an up to 2-fold enlarged ER surface area and a 1.5-fold increased cross-sectional cell area. Furthermore, the strains with enlarged ER displayed an attenuated unfolded protein response. These results underline the impact that ER structures have on productivity and support the notion that reprogramming subcellular structures belongs into the toolbox of synthetic biology.

Production of galactosylated complex-type N-glycans in glycoengineered Saccharomyces cerevisiae

Abstract

N-glycosylation is an important posttranslational modification affecting the properties and quality of therapeutic proteins. Glycoengineering in yeast aims to produce proteins carrying human-compatible glycosylation, enabling the production of therapeutic proteins in yeasts. In this work, we demonstrate further development and characterization of a glycoengineering strategy in a Saccharomyces cerevisiae Δalg3 Δalg11 strain where a truncated Man₃GlcNAc₂ glycan precursor is formed due to a disrupted lipid-linked oligosaccharide synthesis pathway. We produced galactosylated complex-type and hybrid-like N-glycans by expressing a human galactosyltransferase fusion protein both with and without a UDP-glucose 4-epimerase domain from Schizosaccharomyces pombe. Our results showed that the presence of the UDP-glucose 4-epimerase domain was beneficial for the production of digalactosylated complex-type glycans also when extracellular galactose was supplied, suggesting that the positive impact of the UDP-glucose 4-epimerase domain on the galactosylation process can be linked to other processes than its catalytic activity. Moreover, optimization of the expression of human GlcNAc transferases I and II and supplementation of glucosamine in the growth medium increased the formation of galactosylated complex-type glycans. Additionally, we provide further characterization of the interfering mannosylation taking place in the glycoengineered yeast strain.

Key points

• Glycoengineered Saccharomyces cerevisiae can form galactosylated N-glycans.

• Genetic constructs impact the activities of the expressed glycosyltransferases.

• Growth medium supplementation increases formation of target N-glycan structure.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11727-8.

Early Emergence of Adaptive Mechanisms Sustaining Ig Production: Application to Antibody Therapy

Antibody therapy, where artificially-produced immunoglobulins (Ig) are used to treat pathological conditions such as auto-immune diseases and cancers, is a very innovative and competitive field. Although substantial efforts have been made in recent years to obtain specific and efficient antibodies, there is still room for improvement especially when considering a precise tissular targeting or increasing antigen affinity. A better understanding of the cellular and molecular steps of terminal B cell differentiation, in which an antigen-activated B cell becomes an antibody secreting cell, may improve antibody therapy. In this review, we use our recently published data about human B cell differentiation, to show that the mechanisms necessary to adapt a metamorphosing B cell to its new secretory function appear quite early in the differentiation process i.e., at the pre-plasmablast stage. After characterizing the molecular pathways appearing at this stage, we will focus on recent findings about two main processes involved in antibody production: unfolded protein response (UPR) and endoplasmic reticulum (ER) stress. We’ll show that many genes coding for factors involved in UPR and ER stress are induced at the pre-plasmablast stage, sustaining our hypothesis. Finally, we propose to use this recently acquired knowledge to improve productivity of industrialized therapeutic antibodies.