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Etude de la voie de N-Glycosylation et caractérisation de la N-acétylglucosamiltransférase I chez la diatomée Phaeodactylum tricornutum

Abstract : N-glycosylation is a major co- and post-translational event in the protein synthesis. Beside a lot of information in higher eukaryotes, very little is known regarding this pathway in microalgae. In this work, we describe the N-glycosylation pathway of a model diatom, Phaeodactylum tricornutum. First, bio-informatic analysis of its genome revealed the presence of sequences potentially encoding for transferases responsible for the synthesis of the precursor oligosaccharide, some subunits of the oligosaccharyltransferase complex, ER glucosidases and chaperones required for protein quality control, and the Golgi a mannosidase I involved in the trimming of the N-glycan into high mannose-type N-glycan. Moreover, structural analyses of N-linked glycans demonstrated that P. tricornutum endogenous proteins carry mainly high mannose-type N-glycans ranging from Man-5 to Man 9. However, a minor population of more mature N-glycans were also detected, in particular Man3FucGlcNAc2. Consistently, one gene potentially encoding for a N acetylglucosaminyltransferase I (GnT I), a Golgi glycosyltransferase that initiates the formation of complex-type N-glycans, was predicted in the diatom genome. We demonstrated that the GnT I gene encodes for an active protein which is able to restore complex-type N glycan maturation in the Chinese Hamster Ovary Lecl mutant, defective in its endogeneous GnT I activity. Furthermore, study of the GnT I expression in P. tricornutum according to culture conditions, morphotype and strain revealed the presence of GnT I transcripts. Taken together, all these data suggest the occurrence of a GnT I dependent N-glycosylation pathway in P. tricornutum.
Keywords : Microalgae
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Bérengère Baïet. Etude de la voie de N-Glycosylation et caractérisation de la N-acétylglucosamiltransférase I chez la diatomée Phaeodactylum tricornutum. Biochimie [q-bio.BM]. Université de Rouen, 2013. Français. ⟨tel-02053590⟩

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