In plant glycoproteins

The patatin family consists of various glycoproteins in plants making up more than 40% of the total soluble protein in potato tubers. Patatins serve as storage proteins and it has been demonstrated that they exhibit both lipid acyl hydrolase and acetyl transferase activities, which might be involved in tissue wounding responses. Further, recent studies report on antioxidant activities of the major potato allergen Sola t 1 (Seppala et al. 2000). 

The role of undecaprenyl phosphate (C55, allylic) as a carrier of glycosyl units in the biosynthesis of bacterial cells walls is well established. Dolichyl phosphate plays a similar role in the synthesis of glycoproteins in animal systems. Evidence that prenyl lipids serve as glycosyl carriers in the biosynthesis of glycoproteins in plants is accumulating rapidly (Pont Lezica et al., 1976 Delmer al., 1978 Erickson et al., 1978). Several authors have recently reviewed the literature on the role of polyprenols as glycosyl carriers in plants (Hemming, 1978 Pont Lezica, 1979 Elbein, 1979). 

A linkage involving 4-hydroxy-L-proline and L-arabinose has been detected in glycoproteins of plant origin, and it is also possible that L-cys-teine is part of a carbohydrate-protein linkage. Of the types of linkages just mentioned, which have been extensively discussed in reviews,2-9 only the first three have been the subject of synthetic studies, and it is this aspect of the work that will be discussed in the present Chapter. 

Plant-based production systems are now being used commercially for the synthesis of foreign proteins [1-3]. Post-translational modification in plant cells is similar to that carried out by animal cells plant cells are also able to fold multimeric proteins correctly. The sites of glycosylation on plant-produced mammalian proteins are the same as on the native protein however, processing of N-linked glycans in the secretory pathway of plant cells results in a more diverse array of glycoforms than is produced in animal expression systems [4]. Glycoprotein activity is retained in plant-derived mammalian proteins. 

Most therapeutic proteins are glycoproteins, and in this chapter we discuss the advantages and limitations of glycosylation when mammalian proteins and particularly antibodies are produced in plant expression systems. 

The laccase molecule is a dimeric or tetrameric glycoprotein, which contains four copper atoms per monomer, distributed in three redox sites. More than 100 types of laccase have been characterized. These enzymes are glycoproteins with molecular weights of 50-130 kDa. Approximately 45% of the molecular weight of this enzyme in plants are carbohydrate portions, whereas fungal laccases contain less of a carbohydrate portion (10-30%). Some studies have suggested that the carbohydrate portion of the molecule ensures the conformational stability of the globule and protects it from proteolysis and inactivation by radicals (Morozova and others 2007). 

HoodKR, BaasiriRA, Fritz SE, Hood EE. Biochemical and tissue print analyses of hydroxyprohne-rich glycoproteins in cell walls of sporophytic maize tissues. Plant Physiol 1991 96 1214-1219. 

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