N‐linked oligosaccharide processing is not necessary for glycoprotein secretion in plants

Abstract

The role of N-glycans in the secretion of glycoproteins by suspension-cultured sycamore cells was studied. The transport of glycoproteins to the extracellular compartment was investigated in the presence of a glycan-processing inhibitor, castanospermine. Castanospermine has been selected because it inhibits homogeneously glycan maturation in sycamore cells and leads to the accumulation of a single immature N-glycan. The structure of this glycan has been identified as Glc3Man7GlcNAc2 by labeling experiments, affinity chromatography on concanavalin A-Sepharose and proton NMR. In contrast with previous results showing that N-glycosylation is a prerequisite for secretion of N-linked glycoproteins, this secretion is not affected by the presence of castanospermine. As a consequence, the presence of this unprocessed glycan is sufficient for an efficient secretion of glycoproteins in the extracellular compartment of suspension-cultured sycamore cells.

The Golgi apparatus of the scaly green flagellate Scherffelia dubia : uncoupling of glycoprotein and polysaccharide synthesis during flagellar regeneration

“…c, chloroplast; cw, cell wall; f,¯agellum; G, Golgi stack; n, nucleus; sr, scale reticulum. Bars = 0.5 lm b Scale reticulum at 0 min and scale reticulum and multi-scale vesicles at 120 min might require N-glycosylation but not processing to complex glycans (Lerouge et al 1996). However, this might be not a general phenomenon because some glycoproteins are still secreted when N-glycosylation is inhibited (Capkova et al 1997).…”

Fusion with HDEL Protects Cell Wall Invertase from Early Degradation when N-glycosylation is Inhibited

“…Endogenous tobacco and recombinant carrot cell wall invertases were immunoprecipitated from the microsomal (MI) and extracellular (MEX) protein extracts, analysed by SDS-PAGE and fluorography. obtained in different suspension-cultured plant cells clearly show that N-glycans are absolutely required for transport of glycoproteins to the cell surface (Hori and Elbein 1981, Faye and Chrispeels 1989, Driouich et al 1989) regardless of their oligosaccharide structure (Lerouge et al 1996).…”

“…However, when N-glycosylation is prevented, an inhibition of glycoprotein transport to the cell surface is generally observed (Hori et al 1984, Ravi et al 1986, Driouich et al 1989, Faye and Chrispeels 1989 and a degradation of nonglycosylated extracellular glycoproteins takes place when the latter are transported without their N-glycans along the secretory pathway (Faye and Chrispeels 1989). Interestingly, the transport of plant glycoproteins to the cell surface is not affected if the maturation of their N-glycans is prevented by castanospermine (Lerouge et al 1996). Thus, the presence of N-glycans is necessary for an efficient transport of plant glycoproteins to the extracellular compartment independently of their oligosaccharide structure.…”

Uncovering Secretory Secrets

“…Pulse chase experiments using ER glucosidase inhibitors in developing cotyledons or plant cell cultures have failed to show adverse in vivo effects on protein intracellular transport (Chrispeels and Vitale, 1985;Lerouge et al, 1996). Plant calnexin (Huang et al, 1993) and calreticulin (Denecke et al, 1995) have been cloned, and interactions have been shown between calnexin and the newly synthesized subunits of vacuolar H ϩ -ATPase (Li et al, 1998) and between calreticulin and BiP (Crofts et al, 1998).…”

“…Indeed, several plant embryogenesis mutants are affected in other aspects of the secretory pathway, providing support for the notion that its full integrity is critical for plant life (reviewed in Sanderfoot et al, 2000;see Lukowitz et al, 2001). The in vivo pulse chase experiments performed previously may have been too limited in both the length of treatment with glucosidase inhibitors and the plant material used to allow the detection of detrimental effects (Chrispeels and Vitale, 1985;Lerouge et al, 1996). It will be interesting to determine if only a few key proteins are affected negatively by the absence of Glc removal or if this is a more general phenomenon.…”