Some new aspects of the molecular structure of Acacia senegal gum (gum arabic)

Churms, Shirley C.; Merrifield, Edwin H.; Stephen, Alistair M.

doi:10.1016/0008-6215(83)88483-3

Cited by 77 publications

(29 citation statements)

References 25 publications

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“…This relatively invariant Hyp-AGs structure with bifurcated side chains is apparently widespread; it is consistent with compositional data from diverse species (16,27,28) and with the fact that AGPs from diverse species selectively co-precipitate with the ␤-Yariv reagent. The six-residue side chain of interferon Hyp-polysaccharide-1 is identical with the gum arabic side chain in the legume Acacia senegal (31) except for the addition of terminal 5-linked Araf in interferon Hyp-polysaccharide-1.…”

Section: Discussionsupporting

confidence: 83%

“…Churms et al (16,27,28) notably suggested a repetitive structure with "AG substituents showing blocks of 1,3-1inked galactan backbone interrupted by periodate susceptible residues (kinked region)." The structure of Ala-Hyppolysaccharide-1 supported the repetitive subunit hypothesis and also suggests that the arabinogalactan structure is highly conserved in both classical AGPs and the less abundant chimeric glycoproteins of the cell surface (29).…”

Section: Discussionmentioning

confidence: 99%

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Plant O-Hydroxyproline Arabinogalactans Are Composed of Repeating Trigalactosyl Subunits with Short Bifurcated Side Chains

Várnai

Lamport

et al. 2010

Journal of Biological Chemistry

104

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Classical arabinogalactan proteins partially defined by type II O-Hyp-linked arabinogalactans (Hyp-AGs) are structural components of the plant extracellular matrix. Recently we described the structure of a small Hyp-AG putatively based on repetitive trigalactosyl subunits and suggested that AGs are less complex and varied than generally supposed. Here we describe three additional AGs with similar subunits. The Hyp-AGs were isolated from two different arabinogalactan protein fusion glycoproteins expressed in tobacco cells; that is, a 22-residue Hyp-AG and a 20-residue Hyp-AG, both isolated from interferon ␣2b-(Ser-Hyp) 20 , and a 14-residue Hyp-AG isolated from (Ala-Hyp) 51 -green fluorescent protein. We used NMR spectroscopy to establish the molecular structure of these Hyp-AGs, which share common features: (i) a galactan main chain composed of two 133 ␤-linked trigalactosyl blocks linked by a ␤-136 bond; (ii) bifurcated side chains with Ara, Rha, GlcUA, and a Gal 6-linked to Gal-1 and Gal-2 of the main-chain trigalactosyl repeats; (iii) a common side chain structure composed of up to six residues, the largest consisting of an136)-unit, both linked to Gal. The conformational ensemble obtained by using nuclear Overhauser effect data in structure calculations revealed a galactan main chain with a reverse turn involving the ␤-136 link between the trigalactosyl blocks, yielding a moderately compact structure stabilized by H-bonds.Hydroxyproline-rich glycoproteins of the cell surface comprise groups of related structural proteins, including the extensins that form cell wall scaffolding networks essential for cytokinesis (1) and the classical arabinogalactan proteins (2) that are largely at the membrane wall interface (3) and have diverse functions (4). O-Hyp 6 glycosylation characterizes the hydroxyproline-rich glycoproteins and is of much interest as it defines molecular properties and, hence, biological function. Arabinogalactan proteins are highly glycosylated mainly with O-Hyp-arabinogalactan polysaccharides (5, 6). Extensins are less highly glycosylated mainly with small O-Hyp arabinooligosaccharides (7,8), whereas the related proline-rich proteins are minimally glycosylated also with arabinooligosaccharides (9). Peptide sequence directs O-Hyp glycosylation by the addition of small oligosaccharides to contiguous Hyp residues and larger acidic arabinogalactan polysaccharides to clustered noncontiguous Hyp (10, 11). For example, clustered Ala-Hyp and Ser-Hyp are typical AGP glycosylation motifs (12), whereas the Hyp residues in repetitive blocks of Ser-Hyp 2 orSer-Hyp 4 are arabinosylated. The "hyperglycosylation" of closely related AGPs complicates their purification, a problem that can be overcome by expressing single individual AGPs as GFP fusion glycoproteins, the hydrophobic GFP tag enabling chromatographic purification (13,14). This approach also allows purification of neoAGPs containing single repeating AGP glycosylation motifs, for example (Ala-Hyp) n or (Ser-Hyp) n , for base-catalyzed peptide bond hydrol...

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Plant O-Hydroxyproline Arabinogalactans Are Composed of Repeating Trigalactosyl Subunits with Short Bifurcated Side Chains

Várnai

Lamport

et al. 2010

Journal of Biological Chemistry

104

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“…There are also alternative proposed structures of some AGPs to our model of long-chain b-1,3-galactan. Tan et al (2010) propose a repetitive main chain of two b-1,3-galactosyl residues and a kink of b-1,6-linked Gal, whereas others postulate a kink (of unknown nature) in the main chain spaced at seven or more Gal residues (Churms et al, 1983;Bacic et al, 1987;Ellis et al, 2010). Although we did not examine the Yariv reactivity of such a kinked main chain, a kink spaced at seven or more residues might not disrupt the helical structure of the main chain, particularly if it is a kink of b-1,6-linked Gal, since the b-1,6-linkage is generally flexible compared with other types of linkages (Rees and Scott, 1971).…”

Section: Discussionmentioning

confidence: 99%

β-Galactosyl Yariv Reagent Binds to the β-1,3-Galactan of Arabinogalactan Proteins

et al. 2013

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Yariv phenylglycosides [1,3,5-tri(p-glycosyloxyphenylazo)-2,4,6-trihydroxybenzene] are a group of chemical compounds that selectively bind to arabinogalactan proteins (AGPs), a type of plant proteoglycan. Yariv phenylglycosides are widely used as cytochemical reagents to perturb the molecular functions of AGPs as well as for the detection, quantification, purification, and staining of AGPs. However, the target structure in AGPs to which Yariv phenylglycosides bind has not been determined. Here, we identify the structural element of AGPs required for the interaction with Yariv phenylglycosides by stepwise trimming of the arabinogalactan moieties using combinations of specific glycoside hydrolases. Whereas the precipitation with Yariv phenylglycosides (Yariv reactivity) of radish (Raphanus sativus) root AGP was not reduced after enzyme treatment to remove a-L-arabinofuranosyl and b-glucuronosyl residues and b-1,6-galactan side chains, it was completely lost after degradation of the b-1,3-galactan main chains. In addition, Yariv reactivity of gum arabic, a commercial product of acacia (Acacia senegal) AGPs, increased rather than decreased during the repeated degradation of b-1,6-galactan side chains by Smith degradation. Among various oligosaccharides corresponding to partial structures of AGPs, b-1,3-galactooligosaccharides longer than b-1,3-galactoheptaose exhibited significant precipitation with Yariv in a radial diffusion assay on agar. A pull-down assay using oligosaccharides cross linked to hydrazine beads detected an interaction of b-1,3-galactooligosaccharides longer than b-1,3-galactopentaose with Yariv phenylglycoside. To the contrary, no interaction with Yariv was detected for b-1,6-galactooligosaccharides of any length. Therefore, we conclude that Yariv phenylglycosides should be considered specific binding reagents for b-1,3-galactan chains longer than five residues, and seven residues are sufficient for cross linking, leading to precipitation of the Yariv phenylglycosides.Arabinogalactan proteins (AGPs) are a type of plant proteoglycans consisting of a Hyp-rich core protein and large arabinogalactan (AG) moieties (Fincher et al., 1983;Nothnagel, 1997). Although there are many molecular species of AGP differentiated by their core proteins, the AG moieties commonly comprise b-1,3-galactan main chains and b-1,6-galactan side chains, to which L-Ara and other auxiliary sugars, such as GlcA, 4-O-methyl-GlcA, L-Fuc, L-Rha, and Xyl, are attached (Fincher et al., 1983;Nothnagel, 1997;Seifert and Roberts, 2007). A commercial product of AGPs prepared from the acacia (Acacia senegal) tree is known as gum arabic and utilized as a food stabilizer. In the Japanese herbal remedy Juzen-Taiho-To, AGs from Astragalus membranaceus are the active ingredient (Majewska-Sawka and Nothnagel, 2000;Kiyohara et al., 2002). In intact plants, AGPs are implicated in various physiological events and serve as extracellular constituents and signaling molecules. For instance, an AGP from stylar transmitting tissue attracts pollen tub...

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“…Indeed, goethite's solubility increases by 6 orders of magnitude when organic acids are added (22). Because Acacia karroo gum has an uronic acid component (23), it is ideally suited for the chemical complexing of iron, which may have taken place when compound glues were made.…”

mentioning

confidence: 99%

Implications for complex cognition from the hafting of tools with compound adhesives in the Middle Stone Age, South Africa

Wadley

Hodgskiss

Grant

2009

Proc. Natl. Acad. Sci. U.S.A.

346

239

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Compound adhesives made from red ochre mixed with plant gum were used in the Middle Stone Age (MSA), South Africa. Replications reported here suggest that early artisans did not merely color their glues red; they deliberately effected physical transformations involving chemical changes from acidic to less acidic pH, dehydration of the adhesive near wood fires, and changes to mechanical workability and electrostatic forces. Some of the steps required for making compound adhesive seem impossible without multitasking and abstract thought. This ability suggests overlap between the cognitive abilities of modern people and people in the MSA. Our multidisciplinary analysis provides a new way to recognize complex cognition in the MSA without necessarily invoking the concept of symbolism.ochre ͉ replications ͉ glue ͉ modern behavior ͉ Ͼ70,000 years ago A rchaeologists often use symbolic material culture as a marker of modern behavior, but few agree on definitions of either term or explore the types of mental architecture required for symbolic innovations. Here, we move away from the contentious issue of symbolism and draw on the combined expertise of cognitive and earth scientists to create a fresh way of recognizing, in the deep past, cognitive abilities that overlap with our own. People today have a capacity for novel, sustained multilevel operations; this ability may have arisen from neural connectivity in part of the prefrontal cortex (1). The capacity may be recognizable in some technologies, and we use compound adhesive manufacture as our example. To demonstrate complex cognition, we must show that some executive steps required for compound adhesive manufacture are not possible without mental abilities of the kind implied in the ninth subsystem of the Barnard et al. (2) model of mental architecture. Here, abstract meanings and sophisticated organization of action sequences determine decision making. An earlier eighth subsystem would have been mentally incapable of processing 2 levels of meaning simultaneously or of generating fully abstract concepts about behavior.The use of simple (1-component) adhesives is ancient; for example, birch-bark tar was found on 2 flakes from Ϸ200,000 years (200 ka) ago at a site in Italy (3). At Ϸ40 ka, bitumen was found on stone tools in Syria (4), and a similarly aged site in Kenya yielded tools with red ochre stains that imply the use of multicomponent glue (5). Traces of even earlier (Ϸ70 ka) compound adhesives occur, together with microfractures consistent with hafting, on Middle Stone Age (MSA) stone tools from Sibudu Cave, South Africa (see SI Text and Table S1). Several recipes are evident: sometimes plant gum and red ochre (natural iron oxide-hematite-Fe 2 O 3 ) traces (Fig. 1) occur on tool portions that were once inserted in hafts (6-10). Other tools have brown plant gums and black or white fat, but no ochre ( Fig. 1 and SI Text).We acknowledge the possibility that people at Sibudu colored some of their weapons symbolically, perhaps to signify the blood of prey, but we do n...

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Some new aspects of the molecular structure of Acacia senegal gum (gum arabic)

Cited by 77 publications

References 25 publications

Plant O-Hydroxyproline Arabinogalactans Are Composed of Repeating Trigalactosyl Subunits with Short Bifurcated Side Chains

Plant O-Hydroxyproline Arabinogalactans Are Composed of Repeating Trigalactosyl Subunits with Short Bifurcated Side Chains

β-Galactosyl Yariv Reagent Binds to the β-1,3-Galactan of Arabinogalactan Proteins

Implications for complex cognition from the hafting of tools with compound adhesives in the Middle Stone Age, South Africa

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