Substitution of
            <scp>l</scp>
            -Fucose by
            <scp>l</scp>
            -Galactose in Cell Walls of
            <b>
              <i>Arabidopsis mur1</i>
            </b>

Zablackis, Earl; York, William S.; Pauly, Markus; Hantus, Stephen; Reiter, Wolf‐Dieter; Chapple, Clint; Albersheim, Peter; Darvill, Alan G.

doi:10.1126/science.272.5269.1808

Cited by 140 publications

(93 citation statements)

References 23 publications

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“…The murl mutant of Arabidopsis which is completely deficient in L-fucose in the aerial parts of the plant exhibits cell walls that are more fragile than wild type (Reiter et al, 1993). Recent chemical analyses of the tour1 XG indicate that L-galactose partially substitutes for L-fucose (Zablackis et al, 1995). However, it is evident that loss of a fucosylated trisaccharide sidechain on XG does result in a reduction in cell wall strength, suggesting a potential role for fucosylated XG in this respect.…”

Section: Introductionmentioning

confidence: 99%

Xyloglucan sidechains modulate binding to cellulose during in vitro binding assays as predicted by conformational dynamics simulations

1997

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SummaryCross-links between cellulose microfibrils and xyloglucan (XG) molecules play a major role in defining the structural properties of plant cell walls and the regulation of growth and development of dicotyledonous plants. How these cross-links are established and how they are regulated has yet to be determined. In a previous study, preliminary data were presented which suggested that the different sidechains of XG may play a role in controlling cellulose microfibriI-XG interactions. In this study, this question is addressed directly by analyzing to what extent the different sidechains of pea cell wall XG and nasturtium seed storage XG affect their binding to cellulose microfibrils. Of particular importance to this study are the chemical data indicating that pea XG possesses a trisaccharide sidechain, which is not found in nasturtium XG. To this end, conformational dynamic simulations have been used to predict whether oligosaccharides representative of pea and nasturtium XG can adopt a hypothesized cellulosebinding conformation and which of these XGs exhibits a preferential ability to bind cellulose. Extensive analysis of the conformational forms populated during 300 K and high-temperature Monte Carlo simulations established that a planar, sterically accessible, glucan backbone is essential for optimal cellulose-binding. For the trisaccharide sidechain-containing oligosaccharide as found in pea XG, sidechain orientation appeared to regulate the gradual acquisition of this hypothesized cellulose binding conformation. Thus, conformational forms were identified that included the twisted backbone (non-planar) putative solution form of XG, forms in which the trisaccharide sidechain orientation enables increased backbone planarity and steric accessibility, and finally a planar, sterically accessible, backbone. By applying these conformational requirements for cellulose binding, it has been Received 25 May 1996; revised 11 October 1996; accepted 12 November 1996. *For correspondence (fax +1 303 492 7744; e-mail levy@spot.colorado.edu).determined that pea XG possesses a two-to threefold occurrence of the cellulose binding conformation than nasturtium XG. Based on this finding, it was predicted that pea XG would bind to cellulose at a higher rate than nasturtium XG. In vitro binding assays showed that pea XG-avicel binding does indeed occur at a twofold higher rate than nasturtium XG-avicel binding. The enhanced ability of pea cell wall XG over nasturtium seed storage XG to associate with cellulose is consistent with a structural role of the former during epicotyl growth where efficient association with cellulose is a requirement. In contrast, the relatively low ability of nasturtium XG to bind cellulose is consistent with the need to enhance the accessibility of this polymer to glycanases during germination. These findings suggest potential roles for XG sidechain substitution, enabling XG to function in a variety of different biological contexts.

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Section: Introductionmentioning

confidence: 99%

Xyloglucan sidechains modulate binding to cellulose during in vitro binding assays as predicted by conformational dynamics simulations

1997

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“…These include the recently identified MUR genes of Arabidopsis, which were identified through altered leaf sugar composition (Reiter et al, 1993(Reiter et al, , 1997Zablackis et al, 1996;Bonin et al, 1997;Burget and Reiter, 1999). Because several of the mur mutants have lower Fuc and/or Rha levels (mur1, mur2, mur8, and mur11), we tested them with our Ruthenium red staining assay to see if any had a phenotype similar to mum3 and mum5.…”

Section: Mum3 and Mum5 Affect Mucilage Biosynthesismentioning

confidence: 99%

Isolation and Characterization of Mutants Defective in Seed Coat Mucilage Secretory Cell Development in Arabidopsis

Western¹

2001

Plant Physiology

100

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In Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type producing extracellular pectinaceous mucilage and a volcano-shaped secondary cell wall. Differentiation involves a regulated series of cytological events including growth, cytoplasmic rearrangement, mucilage synthesis, and secondary cell wall production. We have tested the potential of Arabidopsis seed coat epidermal cells as a model system for the genetic analysis of these processes. A screen for mutants defective in seed mucilage identified five novel genes (MUCILAGE-MODIFIED [MUM]1-5). The seed coat development of these mutants, and that of three previously identified ones (TRANSPARENT TESTA GLABRA1, GLABRA2, and APETALA2) were characterized. Our results show that the genes identified define several events in seed coat differentiation. Although APETALA2 is needed for differentiation of both outer layers of the seed coat, TRANSPARENT TESTA GLABRA1, GLABRA2, and MUM4 are required for complete mucilage synthesis and cytoplasmic rearrangement. MUM3 and MUM5 may be involved in the regulation of mucilage composition, whereas MUM1 and MUM2 appear to play novel roles in post-synthesis cell wall modifications necessary for mucilage extrusion.Fertilization of the angiosperm ovule not only results in the development of the embryo and endosperm, but also initiates differentiation of the ovule integuments to form the seed coat. The seed coat consists of multiple specialized cell layers that play important roles in embryo protection and the regulation of germination. One specialization is known as myxospermy, a property of epidermal cells whereby they produce large quantities of pectic polysaccharide (mucilage; Frey-Wyssling, 1976; Grubert, 1981; Boesewinkel and Bouman, 1995). Myxospermy is commonly found in species of the Brassicaceae, Solanaceae, Linaceae, and Plantaginaceae, where mucilage forms a gel-like capsule surrounding the seed upon imbibition. Proposed roles for mucilage include facilitating seed hydration and/or dispersal. Mucilages are also found in the root cap and transmitting tract (Frey-Wyssling, 1976; Esau, 1977), where they foster root tip and pollen tube growth, respectively.Mucilages are largely composed of pectins, a heterogeneous group of complex, acidic polysaccharides that also comprise the majority of the plant cell wall matrix. Dicotyledonous pectins largely consist of poly-GalUA (PGA) and rhamnogalacturonan I (RG I; Brett and Waldron, 1990; Carpita and Gibeaut, 1993; Cosgrove, 1997). PGA is composed of an unbranched chain of ␣1,4-linked GalUA residues, whereas RG I is a highly branched polysaccharide with a backbone of alternating ␣1,4-linked GalUA and ␣1,2-linked rhamnose (Rha), with sugar side chains attached to the Rha residues (Brett and Waldron, 1990). The degree of gelling of pectins is largely dependent on ionic bonding between PGA molecules and free divalent calcium. Thus, cell wall fluidity is affected by the degree of methyl esterification of...

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“…Mutations of the mur1 gene produce plants with a nearly complete deficiency of fucose in above-ground tissues and a 40% reduction of fucose in root tissue. Although L-fucose may be replaced by L-galactose to some extent (51), mur1 plants are characterized by markedly dwarfed growth and compromised tensile stem strength (52). The recent structure of apo-GMD from E. coli (23) established its general tertiary structure, but the absence of crystal structures with bound cofactor or substrate provided little insight into the mechanisms of ligand binding and catalysis.…”

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confidence: 99%

Structure of the MUR1 GDP-Mannose 4,6-Dehydratase from Arabidopsis thaliana: Implications for Ligand Binding and Specificity

et al. 2002

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GDP-D-mannose 4,6-dehydratase catalyzes the first step in the de novo synthesis of GDP-Lfucose, the activated form of L-fucose, which is a component of glycoconjugates in plants known to be important to the development and strength of stem tissues. We have determined the three-dimensional structure of the MUR1 dehydratase isoform from Arabidopsis thaliana complexed with its NADPH cofactor as well as with the ligands GDP and GDP-D-rhamnose. MUR1 is a member of the nucleosidediphosphosugar modifying subclass of the short-chain dehydrogenase/reductase enzyme family, having homologous structures and a conserved catalytic triad of Lys, Tyr, and Ser/Thr residues. MUR1 is the first member of this subfamily to be observed as a tetramer, the interface of which reveals a close and intimate overlap of neighboring NADP + -binding sites. The GDP moiety of the substrate also binds in an unusual syn conformation. The protein-ligand interactions around the hexose moiety of the substrate support the importance of the conserved triad residues and an additional Glu side chain serving as a general base for catalysis. Phe and Arg side chains close to the hexose ring may serve to confer substrate specificity at the O2 position. In the MUR1/GDP-D-rhamnose complex, a single unique monomer within the protein tetramer that has an unoccupied substrate site highlights the conformational changes that accompany substrate binding and may suggest the existence of negative cooperativity in MUR1 function.The 6-deoxy monosaccharide L-fucose is found as a component of glycoconjugates in organisms from bacteria to mammals and has a diverse range of functions. In humans, L-fucose is most notably an important constituent of glycoproteins such as the blood group antigens as well as cell surface carbohydrate ligands of the cell adhesion family of selectins involved in functions such as inflammation and the immune response (1). Among other organisms, L-fucosecontaining glycoconjugates are involved in developmental signaling in Drosophila (2), are critical components of bacterial cell walls where they may play a role in pathogenicity, and among rhizobial organisms, are components of Nod factors, influencing nodulation efficiency and host specificity (3, 4). In plants, L-fucose has important structural functions as a component of glycoproteins and cell wall polysaccharides, such as xyloglucan and rhamnogalacturonans I and II. Xyloglucan molecules cross-link cellulose microfibrils, one of the major load-bearing elements of the cell wall, and may be involved in the regulation of extension growth. It has been proposed that L-fucose may stabilize conformations that effectively bind cellulose (5, 6); however, this hypothesis has recently been challenged on the basis of the normal growth habit and wall strength of an Arabidopsis mutant specifically deficient in xyloglucan fucosylation (7). Although the function of rhamnogalacturonan II is unknown, the presence of fucose appears to be important for formation of the normal borate di-ester cross-linked f...

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Substitution of l -Fucose by l -Galactose in Cell Walls of Arabidopsis mur1

Cited by 140 publications

References 23 publications

Xyloglucan sidechains modulate binding to cellulose during in vitro binding assays as predicted by conformational dynamics simulations

Xyloglucan sidechains modulate binding to cellulose during in vitro binding assays as predicted by conformational dynamics simulations

Isolation and Characterization of Mutants Defective in Seed Coat Mucilage Secretory Cell Development in Arabidopsis

Structure of the MUR1 GDP-Mannose 4,6-Dehydratase from Arabidopsis thaliana: Implications for Ligand Binding and Specificity

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