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The secreted plant N-glycoproteome and associated secretory pathways.

Ruiz-May E, Kim SJ, Brandizzi F, Rose JK - Front Plant Sci (2012)

Bottom Line: Large scale and detailed characterization of N-glycoproteins therefore has considerable potential in better understanding the composition and functions of the cell wall proteome, as well as those proteins that reside in other compartments of the secretory pathway.However, technical developments in the analysis of glycoproteins and the structures the glycans that they bear, as well as valuable comparative analyses with non-plant systems, are providing new insights into features that are common among eukaryotes and those that are specific to plants, some of which may reflect the unique nature of the plant cell wall.In this review we present an overview of the current knowledge of plant N-glycoprotein synthesis and trafficking, with particular reference to those that are cell wall localized.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Cornell University Ithaca, NY, USA.

ABSTRACT
N-Glycosylation is a common form of eukaryotic protein post-translational modification, and one that is particularly prevalent in plant cell wall proteins. Large scale and detailed characterization of N-glycoproteins therefore has considerable potential in better understanding the composition and functions of the cell wall proteome, as well as those proteins that reside in other compartments of the secretory pathway. While there have been numerous studies of mammalian and yeast N-glycoproteins, less is known about the population complexity, biosynthesis, structural variation, and trafficking of their plant counterparts. However, technical developments in the analysis of glycoproteins and the structures the glycans that they bear, as well as valuable comparative analyses with non-plant systems, are providing new insights into features that are common among eukaryotes and those that are specific to plants, some of which may reflect the unique nature of the plant cell wall. In this review we present an overview of the current knowledge of plant N-glycoprotein synthesis and trafficking, with particular reference to those that are cell wall localized.

No MeSH data available.


Related in: MedlinePlus

Overview of the secretory pathway of glycosylated proteins. Glycosylated proteins are transported from ER to cis-Golgi by either bulk flow transport or receptor mediated transport. COPII and COPI proteins are involved in anterograde and retrograde trafficking between ER and Golgi, respectively. Secretory and vacuolar proteins are sorted at TGN. Vacuolar proteins in TGN are transported to vacuole via prevacuolar compartment (PVC) formed from maturation of TGN as well as late PVC (LPVC). Secretory proteins are accumulated in the secretory vesicles (SV) and delivered to the cell surface. A transport route indicated by dashed arrows represents a hypothetical pathway for GPI-anchored proteins (PMEI1 and PGIP2).
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Figure 2: Overview of the secretory pathway of glycosylated proteins. Glycosylated proteins are transported from ER to cis-Golgi by either bulk flow transport or receptor mediated transport. COPII and COPI proteins are involved in anterograde and retrograde trafficking between ER and Golgi, respectively. Secretory and vacuolar proteins are sorted at TGN. Vacuolar proteins in TGN are transported to vacuole via prevacuolar compartment (PVC) formed from maturation of TGN as well as late PVC (LPVC). Secretory proteins are accumulated in the secretory vesicles (SV) and delivered to the cell surface. A transport route indicated by dashed arrows represents a hypothetical pathway for GPI-anchored proteins (PMEI1 and PGIP2).

Mentions: After the initial glycosylation event involving the addition of Man and Glc residues with transfer of the N-glycan donor on the protein and final deletion of three glucose and one MAN residues, N-glycoproteins carrying Man8GlcNAc2 are delivered from the ER to the cis-Golgi generally via the COPII machinery (Figure 2) using cargo receptors or bulk flow transport (Kuehn et al., 1998; Phillipson et al., 2001). Several soluble cargo receptors have been characterized in mammals and yeasts by mutant analysis. For example, ERGIC-53 and Emp46p/47p are soluble ER resident receptors that interact with the glycosylation motif of soluble cargos, while Erv29p is a cargo receptor that interacts with the ILV motif of glycosylated proteins (Appenzeller et al., 1999; Belden and Barlowe, 2001; Otte and Barlowe, 2004). Both in vitro and in vivo interaction experiments have demonstrated that the absence of these functional cargo receptors leads to defective secretion, suggesting that they are essential for packing soluble cargo into COPII vesicles prior to transport from the ER to the Golgi. Considering their binding specificity for the glycosylation motif, ERGIC-53, and Emp46p/47p could be regarded as a glycosylation checkpoint (Appenzeller et al., 1999; Otte and Barlowe, 2004). Although receptor mediated cargo recruitment by the COPII machinery has not been characterized in plants, delivery of soluble glycoproteins by bulk flow via COPII machinery has been shown in tobacco, using calreticulin without the ER retention signal HDEL (calreticulin ΔHDEL) and α-amylase fused with HDEL (Phillipson et al., 2001). Calreticulin binds to glycosylated proteins for quality control and has the ER retention signal (HDEL) that mediates retrieval from the Golgi to ER. It has been reported that over-expressed calreticulin ΔHDEL is secreted by the default secretory pathway; however, secretion of calreticulin ΔHDEL decreases when COPII machinery is partially inhibited (Phillipson et al., 2001). These results demonstrate the existence of COPII-mediated bulk flow of glycosylated proteins in tobacco. Interestingly, no close homologs of soluble cargo receptors have been identified in plants, although given the conservation of the COPII machinery among eukaryotes, it is reasonable to hypothesize that plants may also have such receptors.


The secreted plant N-glycoproteome and associated secretory pathways.

Ruiz-May E, Kim SJ, Brandizzi F, Rose JK - Front Plant Sci (2012)

Overview of the secretory pathway of glycosylated proteins. Glycosylated proteins are transported from ER to cis-Golgi by either bulk flow transport or receptor mediated transport. COPII and COPI proteins are involved in anterograde and retrograde trafficking between ER and Golgi, respectively. Secretory and vacuolar proteins are sorted at TGN. Vacuolar proteins in TGN are transported to vacuole via prevacuolar compartment (PVC) formed from maturation of TGN as well as late PVC (LPVC). Secretory proteins are accumulated in the secretory vesicles (SV) and delivered to the cell surface. A transport route indicated by dashed arrows represents a hypothetical pathway for GPI-anchored proteins (PMEI1 and PGIP2).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368311&req=5

Figure 2: Overview of the secretory pathway of glycosylated proteins. Glycosylated proteins are transported from ER to cis-Golgi by either bulk flow transport or receptor mediated transport. COPII and COPI proteins are involved in anterograde and retrograde trafficking between ER and Golgi, respectively. Secretory and vacuolar proteins are sorted at TGN. Vacuolar proteins in TGN are transported to vacuole via prevacuolar compartment (PVC) formed from maturation of TGN as well as late PVC (LPVC). Secretory proteins are accumulated in the secretory vesicles (SV) and delivered to the cell surface. A transport route indicated by dashed arrows represents a hypothetical pathway for GPI-anchored proteins (PMEI1 and PGIP2).
Mentions: After the initial glycosylation event involving the addition of Man and Glc residues with transfer of the N-glycan donor on the protein and final deletion of three glucose and one MAN residues, N-glycoproteins carrying Man8GlcNAc2 are delivered from the ER to the cis-Golgi generally via the COPII machinery (Figure 2) using cargo receptors or bulk flow transport (Kuehn et al., 1998; Phillipson et al., 2001). Several soluble cargo receptors have been characterized in mammals and yeasts by mutant analysis. For example, ERGIC-53 and Emp46p/47p are soluble ER resident receptors that interact with the glycosylation motif of soluble cargos, while Erv29p is a cargo receptor that interacts with the ILV motif of glycosylated proteins (Appenzeller et al., 1999; Belden and Barlowe, 2001; Otte and Barlowe, 2004). Both in vitro and in vivo interaction experiments have demonstrated that the absence of these functional cargo receptors leads to defective secretion, suggesting that they are essential for packing soluble cargo into COPII vesicles prior to transport from the ER to the Golgi. Considering their binding specificity for the glycosylation motif, ERGIC-53, and Emp46p/47p could be regarded as a glycosylation checkpoint (Appenzeller et al., 1999; Otte and Barlowe, 2004). Although receptor mediated cargo recruitment by the COPII machinery has not been characterized in plants, delivery of soluble glycoproteins by bulk flow via COPII machinery has been shown in tobacco, using calreticulin without the ER retention signal HDEL (calreticulin ΔHDEL) and α-amylase fused with HDEL (Phillipson et al., 2001). Calreticulin binds to glycosylated proteins for quality control and has the ER retention signal (HDEL) that mediates retrieval from the Golgi to ER. It has been reported that over-expressed calreticulin ΔHDEL is secreted by the default secretory pathway; however, secretion of calreticulin ΔHDEL decreases when COPII machinery is partially inhibited (Phillipson et al., 2001). These results demonstrate the existence of COPII-mediated bulk flow of glycosylated proteins in tobacco. Interestingly, no close homologs of soluble cargo receptors have been identified in plants, although given the conservation of the COPII machinery among eukaryotes, it is reasonable to hypothesize that plants may also have such receptors.

Bottom Line: Large scale and detailed characterization of N-glycoproteins therefore has considerable potential in better understanding the composition and functions of the cell wall proteome, as well as those proteins that reside in other compartments of the secretory pathway.However, technical developments in the analysis of glycoproteins and the structures the glycans that they bear, as well as valuable comparative analyses with non-plant systems, are providing new insights into features that are common among eukaryotes and those that are specific to plants, some of which may reflect the unique nature of the plant cell wall.In this review we present an overview of the current knowledge of plant N-glycoprotein synthesis and trafficking, with particular reference to those that are cell wall localized.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Cornell University Ithaca, NY, USA.

ABSTRACT
N-Glycosylation is a common form of eukaryotic protein post-translational modification, and one that is particularly prevalent in plant cell wall proteins. Large scale and detailed characterization of N-glycoproteins therefore has considerable potential in better understanding the composition and functions of the cell wall proteome, as well as those proteins that reside in other compartments of the secretory pathway. While there have been numerous studies of mammalian and yeast N-glycoproteins, less is known about the population complexity, biosynthesis, structural variation, and trafficking of their plant counterparts. However, technical developments in the analysis of glycoproteins and the structures the glycans that they bear, as well as valuable comparative analyses with non-plant systems, are providing new insights into features that are common among eukaryotes and those that are specific to plants, some of which may reflect the unique nature of the plant cell wall. In this review we present an overview of the current knowledge of plant N-glycoprotein synthesis and trafficking, with particular reference to those that are cell wall localized.

No MeSH data available.


Related in: MedlinePlus