From plant to microalgae glycobiology: Chlamydomonas reinhardtiias a model to understand microalgae N-glycosylation pathway
Elodie Mathieu-Rivet1, Carole Burel1, Carolina Arias2, Bérengère Baïet1, Romain Louvet1, Marie-Christine Kiefer-Meyer1, Michael Hippler3, Patrice Lerouge1, Arsenio Villarejo2, and Muriel Bardor1.
1) Laboratoire Glyco-MEV EA4358, Université de Rouen, IFRMP23, 76821 Mont-Saint-Aignan, France
2) Department of Biology, Universidad Autonoma de Madrid, E-28049, Spain
3) Institute of Plant Biochemistry and Biotechnology, University of M&uumel;nster, D-48143, Germany
N-glycosylation is a major post-translational modification step in the synthesis in Eukaryotes. This process starts in the endoplasmic reticulum (ER) through the transfer of an oligosaccharide precursor, Glc3Man9GlcNAc2, onto specific Asn residues. Then, the oligosaccharide N-linked to Asn (N-glycan) undergoes several maturation steps involving the removal of Glucose (Glc) and Mannose (Man) residues to generate high mannose-type N-glycans, containing from five to nine Man residues and with the same structure in plant and mammalian glycoproteins. Thereafter, these high mannose N-glycans are modified in the Golgi apparatus to generate complex-type N-glycans, which are structurally different in plants, insects and mammals. This structural diversity is introduced by a broad spectrum of specific-organism glycosyltransferases. In particular, the N-acetylglucosaminyltransferase I (GnT I) transfers a first GlcNAc residue on the alpha(1,3)-Man arm of Man5GlcNAc2 and opens the door to the synthesis of complex-type N-glycans. Thereafter, two Man residues are removed, and a second terminal GlcNAc is transferred, thus resulting in a core GlcNAc2Man3GlcNAc2, which is then decorated by organism-specific glycosyltransferases. To get informations about microalgae, we analyzed glycan profiles in several species by Western blots and affinoblots. Additionally, we recently started to characterize the N-glycosylation pathway of Chlamydomonas reinhardtii. First, we took advantage of the recent sequencing data and identified a set of putative sequences for the different key steps of the N-glycan biosynthesis and maturation. We are currently analyzing the detailed N-glycan structures as well as cloning and functionally characterizing these putative glycosidases and glycosyltransferases.
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