A transient tobacco expression system coupled to MALDI-TOF-MS allows validation of the impact of differential targeting on structure and activity of a recombinant therapeutic glycoprotein produced in plants.

Tobacco-based transient expression was employed to elucidate the impact of differential targeting to subcellular compartments on activity and quality of gastric lipase as a model for the production of recombinant glycoproteins in plants. Overall N-linked glycan structures of recombinant lipase were analyzed and for the first time sugar structures of its four individual N-glycosylation sites were determined in situ by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) on a trypsin digest without isolation or deglycosylation of the peptides. Three glycosylation sites contain both complex-type N-glycans and high-mannose-type structures, the fourth is exclusively linked to high-mannose glycans. Although the overall pattern of glycan structures is influenced by the targeting, our results show that the type of glycans found linked to a given Asn residue is largely influenced by the physico-chemical environment of the site. The transient tobacco system combined with MALDI-TOF-MS appears to be a useful tool for the evaluation of glycoprotein production in plants.