A novel and unique protein N-glycosylation pathway in the green alga Chlamydomonas reinhardtii

Carolina Arias1, Amaya Blanco-Rivero1, Elodie Rivet2, Elena Galán1, Cristina Ortega-Villasante1, Michael Hippler3, Patrice Lerouge2, Muriel Bardor2, Flor Martínez1, and Arsenio Villarejo1

1) Department of Biology. Universidad Autónoma de Madrid. E-28049, Madrid. Spain 2) Laboratoire Glyco-MEV EA 4358, Université de Rouen, IFRMP23, 76821 Mont Saint Aignan Cedex, France 3) Institute of Plant Biochemistry and Biotechnology, University of Münster, D-48143, Germany

N-glycosylation is one of the most fundamental protein post-translational modifications in eukaryotes. This process is composed of two main steps. Early N-glycan processing steps occurring in the endoplasmic reticulum (ER) are conserved. In contrast, maturation steps in the Golgi differ among the organisms and give rise to a large variety of organism-specific structures. Little is known about these processes in green algae. Biochemical and genetic dissection of the protein N-glycosylation in Chlamydomonas reinhardtii reveals the absence of enzymes, such as N-acetyl-glucosaminyltransferase I, which is crucial for the complex-type N-glycans formation in plants and animals. However, C. reinhardtii cells do possess enzymes that are known to trim and add sugar residues to the high mannose type N-glycan synthesized in the ER. We have characterized three genes encoding enzymes involved in the maturation of the algal N-glycans. Their products are functional and modify the N-glycans as the proteins move along the Golgi. One of these genes encodes a core α1,3 fucosyl-transferase (CrFT1). The action mode of the CrFT1 as well as its N-glycan acceptor specificity, differ from those showed by its plant orthologs suggesting that Chlamydomonas could synthesize an original and unique glycan N-linked to the endogenous algal proteins that differs from that found in plants. In addition, the expression of the Crft1 gene is strongly regulated by the environmental conditions. As a consequence, Chlamydomonas N-glycoproteins possess unique sugar decorations that change in response to environmental cues. In-depth characterization of the other two genes is now under progress and data will be presented in the congress.

e-mail address of presenting author: carolina.arias@uam.es