Protein Glycosylation: Implications for In Vivo Functions and Therapeutic Applications - Advances in Biochemical Engineering Biotechnology - page 180

agricultural scale at competitive cost, stable integration of foreign DNA into the
plant genome, and ease of storage of transformed lines as seeds under ambient
conditions. A number of groups have expressed antibody fragments, single
chain molecules, full length antibodies and immunoconjugates employing a
variety of toxins with a view to exploit plants as bioreactors for large scale pro-
duction [202, 203]. A potato plant expressing enterotoxin vaccine is found to
elicit antibody response upon oral immunization in mice [204]. The N -linked
core high-Man glycans have identical structures in plants and other eukaryotes.
Complex plant glycans may be quite heterogeneous, but tend to be smaller than
mammalian complex glycans, and differ in the terminal sugar residues. For
example, a Xyl residue linked -linked Man of the glycan core is

frequently found in plants, but not in mammals while SA has not been identified
in plants.As a result of asialylated form, EPO produced in tobacco cells has no in
vivo biological activity, presumably because of its high clearance rate [205]. The
difference in glycosylation pattern of antibodies expressed in plants had no effect
on antigen binding or specificity. But, for human therapy, the presence of plant
specific glycan might increase the immunogenicity of recombinant antibody.
Furthermore, the possibility that patients may develop an allergenic response to
plant-derived glycan moieties such as core

b 1,2 to the b

1,3-linked fucose need to be taken
into account [206]. Enzymatic removals of unwanted glycan groups or the use of
mutant or recombinant plant strains with altered glycosylation pathways are
ways to approach this problem in cases where inappropriate glycosylation affec-
ts the pharmacokinetics, immunogenicity or product efficacy [165, 207].

a

5.1.5
Dictyostelium discoideum

This well known amoeboid organism is used to express heterologous proteins
that are difficult to study in other systems [208].Various cell lines with different
glycosylation capacities have been developed. D. discoideum has been succes-
sfully used to express two parasite proteins, such as malaria circumsporozoite
surface antigen (CSP) [209] and glutathione- S -transferase (GST) from Schisto-
soma japonicum [210].Besides,Rotavirus outer capsid glycoprotein VP7,human
glycoproteins antithrombin III and muscarinic receptor have also been expres-
sed. O -Linked peptides that are formed in D. discoideum are glycosylated at the
same residues in humans,though the sugars added are not always the same.This
shows a separation of recognition and catalytic domains for the glycosylating
enzymes. These studies have assisted in the designation of specific peptide
motifs as potential O -glycosylation sites [211].

5.2
Protein Glycosylation - Nature of Protein and Host Cells

Each eukaryotic host cell has its own characteristic set of glycosylating enzymes,
and thus authentic glycosylation is unlikely to occur in any expression system.