title: Composition, Assembly, and Trafficking of a Wheat Xylan Synthase Complex.
abstract: Xylans play an important role in plant cell wall integrity and have many industrial applications. Characterization of xylan synthase (XS) complexes responsible for the synthesis of these polymers is currently lacking. We recently purified XS activity from etiolated wheat (Triticum aestivum) seedlings. To further characterize this purified activity, we analyzed its protein composition and assembly. Proteomic analysis identified six main proteins: two glycosyltransferases (GTs) TaGT43-4 and TaGT47-13; two putative mutases (TaGT75-3 and TaGT75-4) and two non-GTs; a germin-like protein (TaGLP); and a vernalization related protein (TaVER2). Coexpression of TaGT43-4, TaGT47-13, TaGT75-3, and TaGT75-4 in Pichia pastoris confirmed that these proteins form a complex. Confocal microscopy showed that all these proteins interact in the endoplasmic reticulum (ER) but the complexes accumulate in Golgi, and TaGT43-4 acts as a scaffold protein that holds the other proteins. Furthermore, ER export of the complexes is dependent of the interaction between TaGT43-4 and TaGT47-13. Immunogold electron microscopy data support the conclusion that complex assembly occurs at specific areas of the ER before export to the Golgi. A di-Arg motif and a long sequence motif within the transmembrane domains were found conserved at the NH2-terminal ends of TaGT43-4 and homologous proteins from diverse taxa. These conserved motifs may control the forward trafficking of the complexes and their accumulation in the Golgi. Our findings indicate that xylan synthesis in grasses may involve a new regulatory mechanism linking complex assembly with forward trafficking and provide new insights that advance our understanding of xylan biosynthesis and regulation in plants.
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701.
authors.forename: Nan
authors.initials: N
authors.lastname: Jiang
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Wiemels
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701.
authors.forename: Aaron
authors.initials: A
authors.lastname: Soya
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701.
authors.forename: Rebekah
authors.initials: R
authors.lastname: Whitley
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701.
authors.forename: Michael
authors.initials: M
authors.lastname: Held
authors.affiliation: Department of Environmental and Plant Biology (N.J., R.E.W., A.S., R.W., A.F.) and Department of Chemistry and Biochemistry (M.H.), Ohio University, Athens, Ohio 45701 faik@ohio.edu.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Faik
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D015151:Immunoblotting; D042541:Intracellular Space / Q000378:metabolism; D016013:Likelihood Functions; D008861:Microsomes / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D005810:Multigene Family; D010430:Pentosyltransferases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010802:Phylogeny; D010843:Pichia / Q000378:metabolism; D019441:Plant Epidermis / Q000166:cytology; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D021382:Protein Sorting Signals; D021381:Protein Transport; D040901:Proteomics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism / Q000648:ultrastructure; D016415:Sequence Alignment; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology; D014908:Triticum / Q000201:enzymology*
chemical_list: D009097:Multienzyme Complexes; D010940:Plant Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D010430:Pentosyltransferases; C038331:1,4-beta-D-xylan synthase