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Plant Nucleotide Sugar Formation, Interconversion, and Salvage by Sugar Recycling*

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Plant Nucleotide Sugar Formation, Interconversion, and Salvage by Sugar Recycling∗ Maor Bar-Peled1,2 and Malcolm A. O’Neill2 1Department of Plant Biology and 2Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602; email: [email protected], [email protected] Annu. Rev. Plant Biol. 2011. 62:127–55 Keywords First published online as a Review in Advance on nucleotide sugar biosynthesis, nucleotide sugar interconversion, March 1, 2011 nucleotide sugar salvage, UDP-glucose, UDP-xylose, The Annual Review of Plant Biology is online at UDP-arabinopyranose mutase plant.annualreviews.org This article’s doi: Abstract 10.1146/annurev-arplant-042110-103918 Nucleotide sugars are the universal sugar donors for the formation Copyright c 2011 by Annual Reviews. by Oak Ridge National Lab on 05/20/11. For personal use only. of polysaccharides, glycoproteins, proteoglycans, glycolipids, and All rights reserved glycosylated secondary metabolites. At least 100 genes encode proteins 1543-5008/11/0602-0127$20.00 involved in the formation of nucleotide sugars. These nucleotide ∗ Annu. Rev. Plant Biol. 2011.62:127-155. Downloaded from www.annualreviews.org Dedicated to Peter Albersheim for his inspiration sugars are formed using the carbohydrate derived from photosynthesis, and his pioneering studies in determining the the sugar generated by hydrolyzing translocated sucrose, the sugars structure and biological functions of complex carbohydrates. released from storage carbohydrates, the salvage of sugars from glycoproteins and glycolipids, the recycling of sugars released during primary and secondary cell wall restructuring, and the sugar generated during plant-microbe interactions. Here we emphasize the importance of the salvage of sugars released from glycans for the formation of nucleotide sugars. We also outline how recent studies combining biochemical, genetic, molecular and cellular approaches have led to an increased appreciation of the role nucleotide sugars in all aspects of plant growth and development. Nevertheless, our understanding of these pathways at the single cell level is far from complete. 127 low-molecular-weight molecules that exist as Contents their glycosides. This diversity of structure is also reflected in a multiplicity of functions. INTRODUCTION.................. 128 Glycans including chloroplastic starch and THE BASIS FOR NUCLEOTIDE cytosolic inulin serve as storage polysaccha- SUGAR AND GLYCAN rides, whereas glycoproteins, proteoglycans, DIVERSITY...................... 128 and glycolipids are typically present at the A BRIEF HISTORY OF cell surface where their functions vary from NUCLEOTIDE SUGARS . 131 catalytic activities to maintaining membrane NUCLEOTIDE SUGAR integrity and recognition. Much of the glycan SYNTHESIS...................... 132 in a plant is present in the wall that surrounds “SLOPPY”: A PROMISCUOUS each cell. The primary wall of growing UDP-SUGAR plant cells is comprised predominantly of PYROPHOSPHORYLASE........ 133 polysaccharides (cellulose, hemicelluloses, FORMATION OF SPECIFIC and pectin) together with smaller amounts NUCLEOTIDE SUGARS IN of glycoprotein, proteoglycan, phenols, and PLANTS.......................... 133 minerals. In lignified secondary walls, glycans UDP-α-D-Glucose................ 133 (cellulose and hemicellulose) account for up to ADP-α-D-Glucose................. 136 70% of a plant’s biomass and are a potential TDP- and GDP-α-D-Glucose...... 136 source of sugar for the production of biofuels UDP-N-Acetyl-α-D-Glucosamine . 137 and renewable chemicals. These cell walls UDP-α-D-Galactose............... 137 provide mechanical support to cells, tissues, UDP-α-D-Glucuronic Acid . 138 and organs and also have a role in regulating UDP-α-D-Xylose.................. 139 plant growth and development. The cell wall UDP-β-L-Arabinopyranose and also forms the interface between the plant and UDP-β-L-Arabinofuranose. 140 its environment and thus has an important UDP-α-D-Galacturonic Acid . 141 role in a plant’s interactions with symbionts, UDP-β-L-Rhamnose.............. 142 pathogens, and abiotic factors. UDP-α-D-Apiose . 143 Understanding plant glycan structures and GDP-α-D-Mannose............... 143 functions as well as developing technologies to GDP-β-L-Fucose.................. 144 increase the commercial value of these com- GDP-L-Galactose.................. 144 plex carbohydrates require knowledge of the CMP-D-Kdo...................... 144 by Oak Ridge National Lab on 05/20/11. For personal use only. enzymes and the corresponding genes involved Rare and Modified Nucleotide in glycan synthesis and modification. In this ar- Sugars.......................... 145 ticle we review the current knowledge of the REGULATION OF NUCLEOTIDE Annu. Rev. Plant Biol. 2011.62:127-155. Downloaded from www.annualreviews.org formation of nucleotide sugars, which serves as SUGAR BIOSYNTHESIS . 146 the primary building block for glycan synthesis. THEFATEOFNDPAFTER SUGAR TRANSFER . 146 FUTURE CHALLENGES . 146 THE BASIS FOR NUCLEOTIDE SUGAR AND GLYCAN DIVERSITY Carbohydrate: used Nucleotide sugars are activated sugar donors interchangeably with and the major precursors for glycan synthesis sugar, a saccharide INTRODUCTION as they are “high energy bond” compounds (monosaccharide, Plants synthesize diverse carbohydrate- (G◦> −7 Kcal/mol) with a high group trans- oligosaccharide, containing molecules (glycans) including fer potential that is used to form a glycosidic polysaccharide) or glycan glycoproteins, proteoglycans, glycolipids, and bond. Various types of nucleotide sugars exist polysaccharides as well as a large number of in nature (Figure 1a) with the majority of the 128 Bar-Peled · O’Neill ab β UDPα-D-Glc O 1,4-linked -D-xylan CH OH OH OH 2 O NH OH O O OH O HO OH O HO O O HO O O HO OH N O O OOP P O CH2 O HO HO O– O– HO OUDP UDP-α-D-Xyl β-1,4-xylosyltransferase OH OH UDP GDP-β-L-Fuc O N O OH OH NH HO OH O O OH O HO O O O O HC HO O HO HO O H3C O OOP P O CH N NH 2 O N 2 COOH O – – OH OH O O HO HO HO OH OUDP OH OH UDP-α-D-GlcA α-1,2-glucuronosyltransferase β CMP- -D-Kdo NH2 UDP N COOH HO COOH HO O OH O O HO OH OH N O O OH O O OH HO P OO CH2 HO O O O O O HO O HO O HOOC O– HO OH OH OH Glucuronoxylan Figure 1 (a) Structures of a representative UDP-sugar (UDP-glucose, UDP-Glc), a GDP-sugar (GDP-fucose, GDP-Fuc), and an NMP-sugar (CMP-Kdo) that are formed by plants. (b) A schematic representation of the reactions involving UDP-sugars and glycosyltransferases in the synthesis of the plant polysaccharide glucurononxylan. One glycosyltransferase transfers a xylose moiety from UDP-Xyl to the xylan backbone acceptor and a different glycosyltransferase transfers a GlcA moiety from UDP-GlcA to the backbone. The mechanism shown depicts glycan extension by the addition of a new sugar to the nonreducing end of the backbone. However, other mechanisms including extension at the reducing end have been proposed (170). sugars linked to a nucleotide-diphosphate monosaccharides can be linked together and (NDP-sugars). However, a limited number the different forms and configurations in which of activated sugars exist as the nucleotide- a monosaccharide can exist: monophosphate (NMP-sugar) configuration. A glycose may exist in either of two abso- by Oak Ridge National Lab on 05/20/11. For personal use only. Other activated sugars including the polyiso- lute configurations (D or L). prenyl phosphate-sugars and the polyisoprenyl A glycose may exist in either a pyranose di-phosphate-sugars exist but are not covered ( p) or furanose ( f ) ring form. Glycan: individual or Annu. Rev. Plant Biol. 2011.62:127-155. Downloaded from www.annualreviews.org in this review. chains of linked The biosynthesis of glycans requires many A glycose may have either of two monosaccharides that α β different nucleotide sugars and the activity of a anomeric configurations ( or ). may or may not be group of enzymes individually known as glyco- A glycosidic linkage may be formed be- attached to another tween the hydroxyl on C-1 of one sugar molecule (e.g., protein, syltransferases (GT). In general, a GT transfers lipid, flavonoid) a sugar from its activated donor to an appropri- and any of the other hydroxyl groups (1→2, 1→3, 1→4, 1→6) on another Glycoprotein: ate glycan acceptor, leading to extension of the a protein containing glycan polymer (Figure 1b). The specificity of sugar. sugars (<10%) linked the individual GTs together with the diversity A glycan may be linear or branched. to an asparagine of activated sugar donors allows an organism A glycan may be modified with noncar- (N-linked) or a hydroxy-amino acid to synthesize many different glycan structures. bohydrate substituents (e.g., O-acetyl (O-linked) in a The ability to form structurally diverse glycans esters, O-methyl ethers, amino acids, polypeptide chain results in large part from the many ways sulfates, and phosphoesters). www.annualreviews.org • Nucleotide Sugar Biosynthesis 129 HO CH2OH CH2OH a CH2OH CH2OH O O HO O H3C O OUDP HO OH β-D-Fruf HO HO HO NAc NAc HO OUDP OUDP OH CH2OH HO CH2OH O UDP-α-D-GalNAc UDP-α-D-GlcNAc UDP-β-L-Rha O HO HO b OH OH HO CH2OH CH OH HO OH O O 2 HO O HO H3C O CH OH OH OH OGDP 2 HO Sucrose HO HO β-D-Fru-(2,1)-α-D-Glc OH OH HO OH OUDP OUDP OH HO UDP-α-D-Gal UDP-α-D-Glc Myo-inositol GDP-β-L-Fuc O HO COOH HOH2C OH O COOH CH2OH OUDP HO O HOH2C O OH O OGDP HO HO OH HO OH HO HO OH OH OH OUDP OUDP HO OGDP UDP-β-L-Galf UDP-α-D-GalA UDP-α-D-GlcA GDP-β-L-Gul GDP-α-D-Man HO CH2OH O O O O HOCH HO 2 O OGDP HOH C OH OUDP 2 OUDP HO HO OH OH OH HO OH OUDP OUDP OH OH HO UDP-β-L-Araf UDP-β-L-Ara UDP-α-D-Xyl UDP-α-D-Apif GDP-β-L-Gal CH2OH HO COOH c HO COOH OH COOH O O HO O O O HO OCMP OH OH HO HO H3C COOH COOH OH OH OH CMP-β-D-Kdo β-D-Dha β-L-AcefA Ascorbate Figure 2 The nucleotide sugars used by plants for the synthesis of glycans.
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