Proteomic Analysis of N-glycoproteins in Arabidopsis

Asparagine (Asn/N)-linked glycans carry the crucial information for protein folding, sorting, transport and degradation. The biochemical pathway for generating such a code is highly conserved in eukaryotic organisms and consists of ordered assembly of a lipid-linked tetradeccasaccharide. With the glycoprotein correctly folded and secreted from the ER to their final destination, the attached N-glycans on the asparagine residues are further trimmed and maturated from high mannose type to complex type. Although many studies have proved the N-glycan is essential for protein stability, targeting and functioning, little is known about the biological roles of the stepwise maturation of N-glycan in plant. Here, we employed a label-free quantitative proteomic method to observe the proteins stability under different N-glycan structure background. The results showed that a total of 570 glycoproteins were determined. Gene ontology analysis revealed proteins involved in signaling and response to stimulus were significantly varied. In addition, the comparasion between protein profiles under different N-glycan structure found that some protein abundance or stability heavily relied on the appearance of the specific N-glycan. That is, protein might express increased with a glycan structure but decreased upon the glycan changed. Our results provided a direct evidence that N-glycan is required for protein stability and the glycan stepwise maturation might be a regulator switch to manipulate specific protein expression especially when the cells suffer the outer stress. Experimental assessment will help decipher in detail the real role of N-glycan maturation.