N -Glycosylation of cholera toxin B subunit in Nicotiana benthamiana : impacts on host stress response, production yield and vaccine potential

Plant-based transient overexpression systems enable rapid and scalable production of subunit vaccines. Previously, we have shown that cholera toxin B subunit (CTB), an oral cholera vaccine antigen, is N -glycosylated upon expression in transgenic Nicotiana benthamiana . Here, we found that overexpression of aglycosylated CTB by agroinfiltration of a tobamoviral vector causes massive tissue necrosis and poor accumulation unless retained in the endoplasmic reticulum (ER). However, the re-introduction of N -glycosylation to its original or an alternative site significantly relieved the necrosis and provided a high CTB yield without ER retention. Quantitative gene expression analysis of PDI , BiP , bZIP60 , SKP1 , 26Sα proteasome and PR1a and the detection of ubiquitinated CTB polypeptides revealed that N -glycosylation significantly relieved ER stress and hypersensitive response and facilitated the folding/assembly of CTB. The glycosylated CTB (gCTB) was characterized for potential vaccine use. Glycan profiling revealed that gCTB contained approximately 38% plant-specific glycans. gCTB retained nanomolar affinity to GM1-ganglioside with only marginal reduction of physicochemical stability and induced an anti-cholera holotoxin antibody response comparable to native CTB in a mouse oral immunization study. These findings demonstrated gCTB's potential as an oral immunogen and point to a potential role of N -glycosylation in increasing recombinant protein yields in plants.