arabinofuranose and araban

Mycobacteria are covered in a thick layer of different polysaccharides that helps to avert the innate immune response. Lipoarabinomannan (LAM) and arabinogalactan (AG) are ubiquitously contained in these envelopes, and rapid access to defined oligo- and polysaccharides is essential to elucidate their structural and biological roles. Arabinofuranose (Araf) residues in LAM and AG are connected either via α-1,2-trans linkages that are synthetically straightforward to install or the more challenging β-(1,2-cis) linkages. Herein, it was demonstrated that automated glycan assembly (AGA) can be used to quickly prepare 1,2-cis-β-Araf as illustrated by the assembly of a highly branched arabinan hexasaccharide and a docosasaccharide arabinan (Araf

Topics: Carbohydrate Sequence; Lipopolysaccharides; Mycobacterium tuberculosis; Polysaccharides

An efficient direct phthalic anhydride-mediated one-pot glycosylation method employing anomeric hydroxy arabinofuranose as glycosyl donor and triflic anhydride as activating agent has been developed. This method afforded the desired di- and oligoarabinofuranosides in good yields even in gram scale glycosylation when t-butylphthalic anhydride was used. Moreover, our new method can be further extended to the syntheses of repeating oligoarabinofuranoside and tetradecasaccharide arabinan motif found in mycobacterial cell wall.

Topics: Arabinose; Carbohydrate Conformation; Carbohydrate Sequence; Carbon-13 Magnetic Resonance Spectroscopy; Cell Wall; Glycosylation; Mycobacterium; Phthalic Anhydrides; Polysaccharides; Proton Magnetic Resonance Spectroscopy; Stereoisomerism

A water-soluble gluco-arabinan (PS-II, M(W)∼62 kDa) isolated from the alkaline extract of the endosperm of Caesalpinia bonduc showed the presence of T-Glcp, (1→4)-Glcp, (1→2,3)-Glcp, T-Araf, (1→5)-Araf, (1→2,5)-Araf, and (1→2,3,5)-Araf in a relative proportion of approximately 2:2:2:3:2:1:1. The proposed repeating unit of the polysaccharide possessed a branched backbone of two (1→3)-α-D-glucopyranose followed by four (1→5)-α-L-arabinofuranose residues. In case of two (1→3)-α-D-glucopyranose, branching occurs at O-2 by a same residue terminated by another one at O-4 position. Out of four (1→5)-α-l-arabinofuranose residues, one residue is terminated at O-2 and O-3 by two arabinofuranose residues and another one situated at the adjacent position is terminated at O-2 with same residue, and two (1→5)-α-L-arabinofuranose residues are free from branching and located before and after the two branched arabinofuranose residues. This gluco-arabinan molecule and previously reported arabinan showed similar extent of splenocytes and thymocytes stimulation, but arabinan showed appreciable macrophage activations.

Topics: Animals; Arabinose; Caesalpinia; Cell Proliferation; ISCOMs; Magnetic Resonance Spectroscopy; Mice; Monosaccharides; Plant Extracts; Polysaccharides; Seeds; Single-Cell Analysis; Thymocytes

Branched arabinofuranose pentasaccharide with 2-azidoethyl aglycon was prepared for the first time by [3+1+1] bis-(1,2-cis)-glycosylation of trisaccharide diol with silyl-protected thioglycoside glycosyl donor. The presence of 2-azidoethyl aglycon would enable the preparation of neoglycoconjugates using the click chemistry approaches.

Topics: Arabinose; Azides; Carbohydrate Conformation; Carbohydrate Sequence; Cell Wall; Glycosylation; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Mycobacterium tuberculosis; Oligosaccharides, Branched-Chain; Polysaccharides

Arabinosyltransferases are a family of membrane-bound glycosyltransferases involved in the biosynthesis of the arabinan segment of two key glycoconjugates, arabinogalactan and lipoarabinomannan, in the mycobacterial cell wall. All arabinosyltransferases identified have been found to be essential for the growth of Mycobcterium tuberculosis and are potential targets for developing new antituberculosis drugs. Technical bottlenecks in designing enzyme assays for screening for inhibitors of these enzymes are (1) the enzymes are membrane proteins and refractory to isolation; and (2) the sole arabinose donor, decaprenylphosphoryl-d-arabinofuranose is sparingly produced and difficult to isolate, and commercial substrates are not available. In this study, we have synthesized several analogues of decaprenylphosphoryl-d-arabinofuranose by varying the chain length and investigated their arabinofuranose (Araf) donating capacity. In parallel, an essential arabinosyltransferase (AftC), an enzyme that introduces α-(1→3) branch points in the internal arabinan domain in both arabinogalactan and lipoarabinomannan synthesis, has been expressed, solubilized, and purified for the first time. More importantly, it has been shown that the AftC is active only when reconstituted in a proteoliposome using mycobacterial phospholipids and has a preference for diacylated phosphatidylinositoldimannoside (Ac(2)PIM(2)), a major cell wall associated glycolipid. α-(1→3) branched arabinans were generated when AftC-liposome complex was used in assays with the (Z,Z)-farnesylphosphoryl d-arabinose and linear α-d-Araf-(1→5)(3-5) oligosaccharide acceptors and not with the acceptor that had a α-(1→3) branch point preintroduced.

Topics: Arabinose; Gene Expression; Mycobacterium tuberculosis; Pentosyltransferases; Polysaccharides; Proteolipids

The synthesis of a variety of arabinose derivatives that have been modified at C-5 was achieved from d-arabinose. The 5-fluoro and 5-methoxy compounds were converted into the corresponding farnesyl phosphodiesters as putative chain terminators of mycobacterial arabinan biosynthesis. Biological testing of these materials revealed no effective anti-mycobacterial activity.

Topics: Antitubercular Agents; Arabinose; Mycobacterium; Pentosyltransferases; Polysaccharides

The major cell wall polysaccharide of mycobacteria is a branched-chain arabinogalactan in which arabinan chains are attached to the 5 carbon of some of the 6-linked galactofuranose residues; these arabinan chains are composed exclusively of D-arabinofuranose (Araf) residues. The immediate precursor of the polymerized Araf is decaprenylphosphoryl-D-Araf, which is derived from 5-phosphoribose 1-diphosphate (pRpp) in an undefined manner. On the basis of time course, feedback, and chemical reduction experiment results we propose that decaprenylphosphoryl-Araf is synthesized by the following sequence of events. (i) pRpp is transferred to a decaprenyl-phosphate molecule to form decaprenylphosphoryl-beta-D-5-phosphoribose. (ii) Decaprenylphosphoryl-beta-D-5-phosphoribose is dephosphorylated to form decaprenylphosphoryl-beta-D-ribose. (iii) The hydroxyl group at the 2 position of the ribose is oxidized and is likely to form decaprenylphosphoryl-2-keto-beta-D-erythro-pentofuranose. (iv) Decaprenylphosphoryl-2-keto-beta-D-erythro-pentofuranose is reduced to form decaprenylphosphoryl-beta-D-Araf. Thus, the epimerization of the ribosyl to an arabinosyl residue occurs at the lipid-linked level; this is the first report of an epimerase that utilizes a lipid-linked sugar as a substrate. On the basis of similarity to proteins implicated in the arabinosylation of the Azorhizobium caulidans nodulation factor, two genes were cloned from the Mycobacterium tuberculosis genome and expressed in a heterologous host, and the protein was purified. Together, these proteins (Rv3790 and Rv3791) are able to catalyze the epimerization, although neither protein individually is sufficient to support the activity.

Topics: Arabinose; Bacterial Proteins; Carbohydrate Epimerases; Diphosphates; Mycobacterium smegmatis; Polyisoprenyl Phosphates; Polysaccharides; Recombinant Proteins; Ribose

The ultrastructure of the spines decorating the cladodes of the cactus Opuntia ficus-indica was investigated by optical microscopy, scanning and transmission electron microscopy, wide angle X-ray, and solid state 13C NMR analyses. Each spine consisted of a compact parallel arrangement of slender cellulosic fibers (0.4 mm in length and 6-10 microm in diameter) with small lumens. The fibers were disencrusted by alkali and sodium chlorite bleaching, yielding a remarkable arabinan-cellulose (1:1) product. X-ray fiber diagrams of the spines before and after purification confirmed the presence of crystalline cellulose domains with molecular axis parallel to the spine axis. CP-MAS 13C T1 NMR data showed a strong interaction at a nanometric level of a fraction of the arabinan and the cellulose crystalline domains. By sequential hydrothermal extractions, followed by a trifluoroacetic acid treatment, a relatively pure cellulose was isolated while the extracted fibers became fibrillated into slender microfibrils having no more than 4-6 nm diameter. The hydrothermal extract yielded the alpha-L-arabinofuranan consisting of a chain of (1-->5)-linked L-arabinosyl residues with branching either at C-2 or C-3 or at both C-2 and C-3. Taken together, these observations suggest that the bulk of the spine fibers consists of an intimate composite of cellulose microfibrils embedded in an arabinan matrix.

Topics: Arabinose; Cellulose; Crystallography, X-Ray; Dietary Fiber; Magnetic Resonance Spectroscopy; Microscopy, Electron; Opuntia; Plant Extracts; Polysaccharides

mAb CS-35 is representative of a large group of antibodies with similar binding specificities that were generated against the Mycobacterium leprae lipopolysaccharide, lipoarabinomannan (LAM), and which cross-reacted extensively with LAMs from Mycobacterium tuberculosis and other mycobacteria. That this antibody also cross-reacts with the arabinogalactan (AG) of the mycobacterial cell wall, suggesting that it recognizes a common arabinofuranosyl (Araf)-containing sequence in AG and LAM, is demonstrated. The antibody reacted more avidly with 'AraLAM' (LAM with naked Araf termini) compared to 'ManLAM' (in which many Araf termini are capped with mannose residues) and mycolylarabinogalactan-peptidoglycan complex (in which the terminal Araf units are substituted with mycolic acids). Neither did the antibody bind to AG from emb knock-out mutants deficient in the branched hexa-Araf termini of AG. These results indicate that the terminal Araf residues of mycobacterial arabinan are essential for binding. Competitive ELISA using synthetic oligosaccharides showed that the branched hexa-Araf methyl glycoside [beta-D-Araf-(1-->2)-alpha-D-Araf-(1-)(2)-(3 and 5)-alpha-D-Araf-(1-->5)-alpha-D-Araf-OCH(3)] was the best competitor among those tested. The related linear methyl glycoside, beta-D-Araf-(1-->2)-alpha-D-Araf-(1-->5)-alpha-D-Araf-(1-->5)-alpha-D-Araf-OCH(3), representing one linear segment of the branched hexa-Araf, was less effective and the other linear tetrasaccharide, beta-D-Araf-(1-->2)-alpha-D-Araf-(1-->3)-alpha-D-Araf-(1-->5)-alpha-D-Araf-OCH(3), was ineffective. The combined results suggest that the minimal epitope recognized by antibody CS-35 encompasses the beta-D-Araf-(1-->2)-alpha-D-Araf-(1-->5)-alpha-D-Araf-(1-->5)-alpha-D-Araf within the branched hexa-Araf motif of mycobacterial arabinans, whether present in LAM or AG.

Topics: Antibodies, Bacterial; Antibodies, Monoclonal; Arabinose; Carbohydrate Conformation; Carbohydrate Sequence; Epitope Mapping; Epitopes; Galactans; Lipopolysaccharides; Mycobacterium smegmatis; Mycobacterium tuberculosis; Polysaccharides

1. The pectic substances of apple have been extracted and separated into a pure pectinic acid and a neutral arabinan-galactan complex by precipitation of the acidic component with ethanol and with cetylpyridinium chloride. 2. The composition of the fractions has been determined. The pectinic acid contained galacturonic acid, arabinose, galactose, rhamnose, xylose and several trace sugars. 3. Transelimination degradation of the pectinic acid gave rise to two components completely separable by zone electrophoresis and by Sephadex gel filtration. Analysis of these components confirmed that the pectinic acid molecules contained long chains of esterified galacturonosyl residues, but showed in addition that more neutral portions containing a high proportion of arabinofuranose residues were attached to them. 4. The identification of rhamnose, galactose and xylose in aldobiouronic acids obtained from a partial hydrolysate of pectinic acid has shown that these sugars are covalently linked in the molecule, and it is suggested that the galacturonosyl-(1-->2)-rhamnose link is a general feature of pectinic acid structure. 5. The possible biological significance of pectinic acid structure has been discussed. 6. The arabinan-galactan complex contained nearly equal quantities of arabinose and galactose residues and some of its physical properties have been investigated.

Topics: Arabinose; Biochemical Phenomena; Biochemistry; Carbohydrates; Chemistry Techniques, Analytical; Chromatography; Chromatography, Gel; Electrophoresis; Esterases; Fruit; Galactose; Hexuronic Acids; Malus; Pectins; Polysaccharides; Research; Ultracentrifugation