Developmental complexity of arabinan polysaccharides and their processing in plant cell walls.
Verhertbruggen, Y., Marcus, S. E., Haeger, A., Verhoef, R., Schols, H. A., McCleary, B. V., McKee, L., Gilbert, H. J. & Knox, J. P. (2009). The Plant Journal, 59(3), 413-425.
Plant cell walls are constructed from a diversity of polysaccharide components. Molecular probes directed to structural elements of these polymers are required to assay polysaccharide structures in situ, and to determine polymer roles in the context of cell wall biology. Here, we report on the isolation and the characterization of three rat monoclonal antibodies that are directed to 1,5-linked arabinans and related polymers. LM13, LM16 and LM17, together with LM6, constitute a set of antibodies that can detect differing aspects of arabinan structures within cell walls. Each of these antibodies binds strongly to isolated sugar beet arabinan samples in ELISAs. Competitive-inhibition ELISAs indicate the antibodies bind differentially to arabinans with the binding of LM6 and LM17 being effectively inhibited by short oligoarabinosides. LM13 binds preferentially to longer oligoarabinosides, and its binding is highly sensitive to arabinanase action, indicating the recognition of a longer linearized arabinan epitope. In contrast, the binding of LM16 to branched arabinan and to cell walls is increased by arabinofuranosidase action. The presence of all epitopes can be differentially modulated in vitro using glycoside hydrolase family 43 and family 51 arabinofuranosidases. In addition, the LM16 epitope is sensitive to the action of β-galactosidase. Immunofluorescence microscopy indicates that the antibodies can be used to detect epitopes in cell walls, and that the four antibodies reveal complex patterns of epitope occurrence that vary between organs and species, and relate both to the probable processing of arabinan structural elements and the differing mechanical properties of cell walls.
Versatile high resolution oligosaccharide microarrays for plant glycobiology and cell wall research.
Pedersen, H. L., Fangel, J. U., McCleary, B., Ruzanski, C., Rydahl, M. G., Ralet, M. C., Farkas, V., Von Schantz, L., Marcus, S. E., Andersen, M.C. F., Field, R., Ohlin, M., Knox, J. P., Clausen, M. H. & Willats, W. G. T. (2012). Journal of Biological Chemistry, 287(47), 39429-39438.
Microarrays are powerful tools for high throughput analysis, and hundreds or thousands of molecular interactions can be assessed simultaneously using very small amounts of analytes. Nucleotide microarrays are well established in plant research, but carbohydrate microarrays are much less established, and one reason for this is a lack of suitable glycans with which to populate arrays. Polysaccharide microarrays are relatively easy to produce because of the ease of immobilizing large polymers noncovalently onto a variety of microarray surfaces, but they lack analytical resolution because polysaccharides often contain multiple distinct carbohydrate substructures. Microarrays of defined oligosaccharides potentially overcome this problem but are harder to produce because oligosaccharides usually require coupling prior to immobilization. We have assembled a library of well characterized plant oligosaccharides produced either by partial hydrolysis from polysaccharides or by de novo chemical synthesis. Once coupled to protein, these neoglycoconjugates are versatile reagents that can be printed as microarrays onto a variety of slide types and membranes. We show that these microarrays are suitable for the high throughput characterization of the recognition capabilities of monoclonal antibodies, carbohydrate-binding modules, and other oligosaccharide-binding proteins of biological significance and also that they have potential for the characterization of carbohydrate-active enzymes.
Roasting-induced changes in arabinotriose, a model of coffee arabinogalactan side chains.
Moreira, A. S. P., Coimbra, M. A., Nunes, F. M. & Domingues, M. R. M. (2013). Food Chemistry, 138(4), 2291-2299.
Thermal processing can promote reactions that change the structure of food constituents, often by unknown mechanisms, such as those occurring in arabinose residues of coffee arabinogalactan side chains. Aiming to know more about these modifications, the structurally related α-(1→5)-L-arabinotriose was roasted at 200°C and the products obtained were identified by ESI-MS and MALDI-MS and characterised by ESI-MSn. Depolymerised and polymerised oligosaccharides with up to 16 residues and new types of linkages were formed. Also, products resulting from dehydration, oxidation, and cleavage of a carbon–carbon bond at the reducing end of the corresponding non-modified oligosaccharide were formed, probably promoting the release of formaldehyde, formic acid, glycolaldehyde, glyoxal, acetic acid, glycolic acid, glyceraldehyde, 2-hydroxypropanedialdehyde and lactic acid. As many of these compounds have been reported to occur in roasted coffee beans and/or brews, it can be suggested that the degradation of coffee arabinogalactan side chains can contribute to their formation upon roasting.
Two distinct arabinofuranosidases contribute to arabino-oligosaccharide degradation in Bacillus subtilis.
Inácio, J. M., Correia, I. L. & de Sá-Nogueira, I. (2008). Microbiology, 154(9), 2719-2729.
Bacillus subtilis produces α-L-arabinofuranosidases (EC 126.96.36.199; AFs) capable of releasing arabinosyl oligomers and L-arabinose from plant cell walls. Here, we show by insertion-deletion mutational analysis that genes abfA and xsa(asd), herein renamed abf2, encode AFs responsible for the majority of the intracellular AF activity in B. subtilis. Both enzyme activities were shown to be cytosolic and functional studies indicated that arabino-oligomers are natural substrates for the AFs. The products of the two genes were overproduced in Escherichia coli, purified and characterized. The molecular mass of the purified AbfA and Abf2 was about 58 kDa and 57 kDa, respectively. However, native PAGE gradient gel analysis and cross-linking assays detected higher-order structures (>250 kDa), suggesting a multimeric organization of both enzymes. Kinetic experiments at 37°C, with p-nitrophenyl-α-L-arabinofuranoside as substrate, gave an apparent Km of 0.498 mM and 0.421 mM, and Vmax of 317 U mg-1 and 311 U mg-1 for AbfA and Abf2, respectively. The two enzymes displayed maximum activity at 50°C and 60°C, respectively, and both proteins were most active at pH 8.0. AbfA and Abf2 both belong to family 51 of the glycoside hydrolases but have different substrate specificity. AbfA acts preferentially on (1→5) linkages of linear α-1,5-L-arabinan and α-1,5-linked arabino-oligomers, and is much less effective on branched sugar beet arabinan and arabinoxylan and arabinogalactan. In contrast, Abf2 is most active on (1→2) and (1→3) linkages of branched arabinan and arabinoxylan, suggesting a concerted contribution of these enzymes to optimal utilization of arabinose-containing polysaccharides by B. subtilis.
A multitask ATPase serving different ABC-type sugar importers in Bacillus subtilis.
Ferreira, M. J. & de Sá-Nogueira, I. (2010). Journal of Bacteriology, 192(20), 5312-5318.
Bacillus subtilis is able to utilize arabinopolysaccharides derived from plant biomass. Here, by combining genetic and physiological analyses we characterize the AraNPQ importer and identify primary and secondary transporters of B. subtilis involved in the uptake of arabinosaccharides. We show that the ABC-type importer AraNPQ is involved in the uptake of α-1,5-arabinooligosaccharides, at least up to four L-arabinosyl units. Although this system is the key transporter for α-1,5-arabinotriose and α-1,5-arabinotetraose, the results indicate that α-1,5-arabinobiose also is translocated by the secondary transporter AraE. This broad-specificity proton symporter is the major transporter for arabinose and also is accountable for the uptake of xylose and galactose. In addition, MsmX is shown to be the ATPase that energizes the incomplete AraNPQ importer. Furthermore, the results suggest the existence of at least one more unidentified MsmX-dependent ABC importer responsible for the uptake of nonlinear α-1,2- and α-1,3-arabinooligosaccharides. This study assigns MsmX as a multipurpose B. subtilis ATPase required to energize different saccharide transporters, the arabinooligosaccharide-specific AraNPQ-MsmX system, a putative MsmX-dependent ABC transporter specific for nonlinear arabinooligosaccharides, and the previously characterized maltodextrin-specific MdxEFG-MsmX system.