Complete genome of a new Firmicutes species belonging to the dominant human colonic microbiota (‘Ruminococcus bicirculans’) reveals two chromosomes and a selective capacity to utilize plant glucans.
Wegmann, U., Louis, P., Goesmann, A., Henrissat, B., Duncan, S. H. & Flint, H. J. (2014). Environmental Microbiology, 16(9), 2879–2890.
The recently isolated bacterial strain 80/3 represents one of the most abundant 16S rRNA phylotypes detected in the healthy human large intestine and belongs to the Ruminococcaceae family of Firmicutes. The completed genome sequence reported here is the first for a member of this important family of bacteria from the human colon. The genome comprises two large chromosomes of 2.24 and 0.73 Mbp, leading us to propose the name Ruminococcus bicirculans for this new species. Analysis of the carbohydrate active enzyme complement suggests an ability to utilize certain hemicelluloses, especially β-glucans and xyloglucan, for growth that was confirmed experimentally. The enzymatic machinery enabling the degradation of cellulose and xylan by related cellulolytic ruminococci is however lacking in this species. While the genome indicated the capacity to synthesize purines, pyrimidines and all 20 amino acids, only genes for the synthesis of nicotinate, NAD+, NADP+ and coenzyme A were detected among the essential vitamins and co-factors, resulting in multiple growth requirements. In vivo, these growth factors must be supplied from the diet, host or other gut microorganisms. Other features of ecological interest include two type IV pilins, multiple extracytoplasmic function-sigma factors, a urease and a bile salt hydrolase.
Role of glycoside phosphorylases in mannose foraging by human gut bacteria.
Ladevèze, S., Tarquis, L., Cecchini, D. A., Bercovici, J., André, I., Topham, C. M., Morel, S., Laville, E., Monsan, P., Lombard, V., Henrissat, B. & Potocki-Véronèse, G. (2013). Journal of Biological Chemistry, 288(45), 32370-32383.
To metabolize both dietary fiber constituent carbohydrates and host glycans lining the intestinal epithelium, gut bacteria produce a wide range of carbohydrate-active enzymes, of which glycoside hydrolases are the main components. In this study, we describe the ability of phosphorylases to participate in the breakdown of human N-glycans, from an analysis of the substrate specificity of UhgbMP, a mannoside phosphorylase of the GH130 protein family discovered by functional metagenomics. UhgbMP is found to phosphorolyze β-D-Manp-1,4-β-D-GlcpNAc-1,4-D-GlcpNAc and is also a highly efficient enzyme to catalyze the synthesis of this precious N-glycan core oligosaccharide by reverse phosphorolysis. Analysis of sequence conservation within family GH130, mapped on a three-dimensional model of UhgbMP and supported by site-directed mutagenesis results, revealed two GH130 subfamilies and allowed the identification of key residues responsible for catalysis and substrate specificity. The analysis of the genomic context of 65 known GH130 sequences belonging to human gut bacteria indicates that the enzymes of the GH130_1 subfamily would be involved in mannan catabolism, whereas the enzymes belonging to the GH130_2 subfamily would rather work in synergy with glycoside hydrolases of the GH92 and GH18 families in the breakdown of N-glycans. The use of GH130 inhibitors as therapeutic agents or functional foods could thus be considered as an innovative strategy to inhibit N-glycan degradation, with the ultimate goal of protecting, or restoring, the epithelial barrier.
A revised architecture of primary cell walls based on biomechanical changes induced by substrate-specific endoglucanases.
Park, Y. B. & Cosgrove, D. J. (2012). Plant Physiology, 158(4), 1933-1943.
Xyloglucan is widely believed to function as a tether between cellulose microfibrils in the primary cell wall, limiting cell enlargement by restricting the ability of microfibrils to separate laterally. To test the biomechanical predictions of this “tethered network” model, we assessed the ability of cucumber (Cucumis sativus) hypocotyl walls to undergo creep (long-term, irreversible extension) in response to three family-12 endo-β-1,4-glucanases that can specifically hydrolyze xyloglucan, cellulose, or both. Xyloglucan-specific endoglucanase (XEG from Aspergillus aculeatus) failed to induce cell wall creep, whereas an endoglucanase that hydrolyzes both xyloglucan and cellulose (Cel12A from Hypocrea jecorina) induced a high creep rate. A cellulose-specific endoglucanase (CEG from Aspergillus niger) did not cause cell wall creep, either by itself or in combination with XEG. Tests with additional enzymes, including a family-5 endoglucanase, confirmed the conclusion that to cause creep, endoglucanases must cut both xyloglucan and cellulose. Similar results were obtained with measurements of elastic and plastic compliance. Both XEG and Cel12A hydrolyzed xyloglucan in intact walls, but Cel12A could hydrolyze a minor xyloglucan compartment recalcitrant to XEG digestion. Xyloglucan involvement in these enzyme responses was confirmed by experiments with Arabidopsis (Arabidopsis thaliana) hypocotyls, where Cel12A induced creep in wild-type but not in xyloglucan-deficient (xxt1/xxt2) walls. Our results are incompatible with the common depiction of xyloglucan as a load-bearing tether spanning the 20- to 40-nm spacing between cellulose microfibrils, but they do implicate a minor xyloglucan component in wall mechanics. The structurally important xyloglucan may be located in limited regions of tight contact between microfibrils.
Mannans and endo-β-mannanases (MAN) in Brachypodium distachyon: expression profiling and possible role of the BdMAN genes during coleorhiza-limited seed germination.
González-Calle, V., Barrero-Sicilia, C., Carbonero, P. & Iglesias-Fernández, R. (2015). Journal of Experimental Botany, 66(13), 3753-3764.
Immunolocalization of mannans in the seeds of Brachypodium distachyon reveals the presence of these polysaccharides in the root embryo and in the coleorhiza in the early stages of germination (12h), decreasing thereafter to the point of being hardly detected at 27h. Concurrently, the activity of endo-β-mannanases (MANs; EC 220.127.116.11) that catalyse the hydrolysis of β-1,4 bonds in mannan polymers, increases as germination progresses. The MAN gene family is represented by six members in the Brachypodium genome, and their expression has been explored in different organs and especially in germinating seeds. Transcripts of BdMAN2, BdMAN4 and BdMAN6 accumulate in embryos, with a maximum at 24–30h, and are detected in the coleorhiza and in the root by in situ hybridization analyses, before root protrusion (germination sensu stricto). BdMAN4 is not only present in the embryo root and coleorhiza, but is abundant in the de-embryonated (endosperm) imbibed seeds, while BdMAN2 and BdMAN6 are faintly expressed in endosperm during post-germination (36–42h). BdMAN4 and BdMAN6 transcripts are detected in the aleurone layer. These data indicate that BdMAN2, BdMAN4 and BdMAN6 are important for germination sensu stricto and that BdMAN4 and BdMAN6 may also influence reserve mobilization. Whether the coleorhiza in monocots and the micropylar endosperm in eudicots have similar functions, is discussed.
Purification and Characterization of a Thermostable β-mannanase from Bacillus subtilis BE-91: Potential Application in Inflammatory Diseases.
Cheng, L., Duan, S., Feng, X., Zheng, K., Yang, Q. & Liu, Z. (2016). BioMed Research International, Article ID 6380147.
β-mannanase has shown compelling biological functions because of its regulatory roles in metabolism, inflammation, and oxidation. This study separated and purified the β-mannanase from Bacillus subtilis BE-91, which is a powerful hemicellulose-degrading bacterium using a “two-step” method comprising ultrafiltration and gel chromatography. The purified β-mannanase (about 28.2 kDa) showed high specific activity (79, 859.2 IU/mg). The optimum temperature and pH were 65°C and 6.0, respectively. Moreover, the enzyme was highly stable at temperatures up to 70°C and pH 4.5-7.0. The β-mannanase activity was significantly enhanced in the presence of Mn+, Cu2+, Zn2+, Ca2+, Mg2+, and Al3+ and strongly inhibited by Ba2+, and Pb2+. Km and Vmax values for locust bean gum were 7.14 mg/mL and 107.5 μmol/min/mL versus 1.749 mg/mL and 33.45 µmol/min/mL for Konjac glucomannan, respectively. Therefore, β-mannanase purified by this work shows stability at high temperatures and in weakly acidic or neutral environments. Based on such data, the β-mannanase will have potential applications as a dietary supplement in treatment of inflammatory processes.
A flexible loop for mannan recognition and activity enhancement in a bifunctional glycoside hydrolase family 5.
Liang, P. H., Lin, W. L., Hsieh, H. Y., Lin, T. Y., Chen, C. H., Tewary, S. K., Lee, H. L., Yuan, S. F., Yang, B., Yao, J. Y. & Ho, M. C. (2017). Biochimica et Biophysica Acta (BBA) - General Subjects, In Press.
Background: An array of glycoside hydrolases with multiple substrate specificities are required to digest plant cell wall polysaccharides. Cel5E from Clostridium thermocellum and Cel5A from Thermotoga maritima are two glycoside hydrolase family 5 (GH5) enzymes with high sequence and structural similarity, but notably possess different substrate specificities; the former is a bifunctional cellulase/xylanase and the latter is a cellulase/mannanase. A specific loop in TmCel5A, Tmloop, is one of the most structurally divergent regions compared to CtCel5E and interacts with substrates, suggesting the importance for mannan recognition. Method: A Tmloop inserted CtCel5E and its related mutants were produced to investigate the role of Tmloop in catalysis. Crystal structure of CtCel5E-TmloopF267A followed by site-direct mutagenesis reveals the mechanism. RtCelB, a homolog with Tmloop was identified to have mannanase activity. Result: Tmloop incorporation enables CtCel5E to gain mannanase activity. Tyr270, His277, and Trp282 in the Tmloop are indispensable for CtCel5E Tmloop catalysis, and weakening hydrophobic environment near the Tmloop enhances enzyme kcat. Using our newly identified loop motif to search for structurally conserved homologs in other subfamilies of GH5, we identified RtCelB. This homolog, originally annotated as a cellulase also possesses mannanase and xylanase activities. Conclusion: Our studies show that Tmloop enhances GH5 enzyme promiscuity and plays a role in catalysis. General significance: The study identified a loop of GH5 for mannan recognition and catalysis. Weakening the hydrophobic environment near the loop can also enhance the enzyme catalytic rate. Our findings provide a new insight on mannan recognition and activity enhancement of GH5.
Trp residue at subsite − 5 plays a critical role in the substrate binding of two protistan GH26 β-mannanases from a termite hindgut.
Hsu, Y., Koizumi, H., Otagiri, M., Moriya, S. & Arioka, M. (2018). Applied Microbiology and Biotechnology, 1-11.
Symbiotic protists in the hindgut of termites provide a novel enzymatic resource for efficient lignocellulytic degradation of plant biomass. In this study, two β-mannanases, RsMan26A and RsMan26B, from a symbiotic protist community of the lower termite, Reticulitermes speratus, were successfully expressed in the methylotrophic yeast, Pichia pastoris. Biochemical characterization experiments demonstrated that both RsMan26A and RsMan26B are endo-acting enzymes and have a very similar substrate specificity, displaying a higher catalytic efficiency to galactomannan from locust bean gum (LBG) and glucomannan than to β-1,4-mannan and highly substituted galactomannan from guar gum. Homology modeling of RsMan26A and RsMan26B revealed that each enzyme displays a long open cleft harboring a unique hydrophobic platform (Trp79) that stacks against the sugar ring at subsite - 5. The Km) values of W79A mutants of RsMan26A and RsMan26B to LBG increased by 4.8-fold and 3.6-fold, respectively, compared with those for the native enzymes, while the kcat) remained unchanged or about 40% of that of the native enzyme, resulting in the decrease in the catalytic efficiency by 4.8-fold and 9.1-fold, respectively. The kinetic values for glucomannan also showed a similar result. These results demonstrate that the Trp residue present near the subsite - 5 has an important role in the recognition of the sugar ring in the substrate.
Biochemical studies of two lytic polysaccharide monooxygenases from the white-rot fungus Heterobasidion irregulare and their roles in lignocellulose degradation.
Liu, B., Olson, Å., Wu, M., Broberg, A. & Sandgren, M. (2017). PloS One, 12(12), e0189479.
Lytic polysaccharide monooxygenases (LPMO) are important redox enzymes produced by microorganisms for the degradation of recalcitrant natural polysaccharides. Heterobasidion irregulare is a white-rot phytopathogenic fungus that causes wood decay in conifers. The genome of this fungus encodes 10 putative Auxiliary Activity family 9 (AA9) LPMOs. We describe the first biochemical characterization of H. irregulare LPMOs through heterologous expression of two CBM-containing LPMOs from this fungus (HiLPMO9H, HiLPMO9I) in Pichia pastoris. The oxidization preferences and substrate specificities of these two enzymes were determined. The two LPMOs were shown to cleave different carbohydrate components of plant cell walls. HiLPMO9H was active on cellulose and oxidized the substrate at the C1 carbon of the pyranose ring at β-1,4-glycosidic linkages, whereas HiLPMO9I cleaved cellulose with strict oxidization at the C4 carbon of glucose unit at internal bonds, and also showed activity against glucomannan. We propose that the two LPMOs play different roles in the plant-cell-wall degrading system of H. irregulare for degradation of softwood and that the lignocellulose degradation mediated by this white-rot fungus may require collective efforts from multi-types of LPMOs.
Purification, characterization, and overexpression of an endo-1,4-β-mannanase from thermotolerant Bacillus sp. SWU60.
Seesom, W., Thongket, P., Yamamoto, T., Takenaka, S., Sakamoto, T. & Sukhumsirichart, W. (2017). World Journal of Microbiology and Biotechnology, 33(3), 53.
Endo-β-1,4-mannanases are important catalytic agents in several industries. The enzymes randomly cleave the β-1,4-linkage in the mannan backbone and release short β-1,4-mannooligosaccharides and mannose. In the present study, mannanase (ManS2) from thermotolerant Bacillus sp. SWU60 was purified, characterized, and its gene was cloned and overexpressed in Escherichia coli. ManS2 was purified from culture filtrate (300 ml) by using hydrophobic, ion-exchange, and size-exclusive liquid chromatography. The apparent molecular mass was 38 kDa. Optimal pH and temperature for enzyme activity were 6.0 and 60°C, respectively. The enzyme was stable up to 60°C for 1 h and at pH 5-9 at 4°C for 16 h. Its enzyme activity was inhibited by Hg+2. The full-length mans2 gene was 1,008 bp, encoding a protein of 336 amino acids. Amino acid sequence analysis revealed that it belonged to glycoside hydrolase family 26. Konjac glucomannan was a favorable substrate for recombinant ManS2 (rManS2). rManS2 also degraded galactomannan from locust bean gum, indicating its potential for production of glucomanno- and galactomanno-oligosaccharides. Both native and recombinant ManS2 from Bacillus sp. SWU60 can be applied in several industries especially food and feed.
An ancient family of lytic polysaccharide monooxygenases with roles in arthropod development and biomass digestion.
Sabbadin , F., Hemsworth, G. R., Ciano, L., Henrissat, B., Dupree, P., Tryfona, T., Marques, R. D. S., Sweeney, S. T., Besser, K., Elias, L., Pesante, G., Li, Y., Dowle, A. A., Bates, R., Gomez, L. D., Simister, R., Davies, G. J., Walton, P. H., Bruce, N. C., McQueen-Mason, S. J. (2018). Nature Communications, In Press.
Thermobia domestica belongs to an ancient group of insects and has a remarkable ability to digest crystalline cellulose without microbial assistance. By investigating the digestive proteome of Thermobia, we have identified over twenty members of an uncharacterized family of lytic polysaccharide monooxygenases (LPMOs). We show that this LPMO family spans across several clades of the Tree of Life, is of ancient origin and was recruited by early arthropods with possible roles in remodelling endogenous chitin scaffolds during development and metamorphosis. Based on our in-depth characterization of Thermobia’s LPMOs, we propose that diversification of these enzymes towards cellulose digestion might have endowed ancestral insects with an effective biochemical apparatus for biomass degradation, allowing the early colonization of land during the Paleozoic Era. The vital role of LPMOs in modern agricultural pests and disease vectors offers new opportunities to help tackle global challenges in food security and the control of infectious diseases.