Virtually nothing is known about the mechanisms and enzymes responsible for the glycosylation of arabinogalactan proteins (AGPs). The glycosyltransferase 37 family contains plant-specific enzymes, which suggests involvement in plant-specific organs such as the cell wall. Our working hypothesis is that AtFUT4 and AtFUT6 genes encode α(1,2)fucosyltransferases (FUTs) for AGPs. Multiple lines of evidence support this hypothesis. First, overexpression of the two genes in tobacco BY2 cells, known to contain nonfucosylated AGPs, resulted in a staining of transgenic cells with eel lectin, which specifically binds to terminal α-linked fucose. Second, monosaccharide analysis by high pH anion exchange chromatography and electrospray ionization mass spectrometry indicated the presence of fucose in AGPs from transgenic cell lines but not in AGPs from wild type cells. Third, detergent extracts from microsomal membranes prepared from transgenic lines were able to fucosylate, in vitro, purified AGPs from BY2 wild type cells. Susceptibility of [14C]fucosylated AGPs to α(1,2)fucosidase, and not to α(1,3/4)fucosidase, indicated that an α(1,2) linkage is formed. Furthermore, dearabinosylated AGPs were not substrate acceptors for these enzymes, indicating that arabinosyl residues represent the fucosylation sites on these molecules. Testing of several polysaccharides, oligosaccharides, and glycoproteins as potential substrate acceptors in the fucosyl transfer reactions indicated that the two enzymes are specific for AGPs but are not functionally redundant because they differentially fucosylate certain AGPs. AtFUT4 and AtFUT6 are the first enzymes to be characterized for AGP glycosylation and further our understanding of cell wall biosynthesis.
cell wall, Fucosyltransferases, Arabidopsis, mass spectrometry (MS), golgi, glycoprotein biosynthesis, arabinogalactan proteins
Publication DOI: 10.1074/jbc.M110.102715Journal NLM ID: 2985121RPublisher: Baltimore, MD: American Society for Biochemistry and Molecular Biology
Correspondence: faik@ohio.edu
Institutions: Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701, Molecular and Cellular Biology Program, Ohio University, Athens, Ohio 45701, Laboratoire “Glycobiologie et Matrice Extracellulaire Végétale”, Université de Rouen, UPRES-EA 4358, IFRMP 23, UFR des Sciences et Techniques, F-76821 Mont-Saint-Aignan, France
Methods: gel filtration, ESI-MS, HPAEC, enzymatic assay, genetic manipulations
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