Complex pectin metabolism by gut bacteria reveals novel catalytic functions
Citation
Ndeh, D., Rogowski, A., Cartmell, A., Luis, A.S., Baslé, A., Gray, J., Venditto, I., Briggs, J., Zhang, X., Labourel, A., Terrapon, N., Buffetto, F., Nepogodiev, S., Xiao, Y., Field, R.A., Zhu, Y., O'Neill, M.A., Urbanowicz, B.R., York, W.S., Davies, G.J., Abbott, D.W., Ralet, M.-C., Martens, E.C., Henrissat, B., Gilbert, H.J. (2017). Complex pectin metabolism by gut bacteria reveals novel catalytic functions, 544(7648), 65-70. http://dx.doi.org/10.1038/nature21725
Plain language summary
This study defines an enzyme pathway from a gut bacteria (Bacteroides thetaiotaomicron) that degrades the most complex carbohydrate in nature (rhamnogalacturonan-II). Although rhamnogalacturonan-II is relatively common, being a primary component of plant cell walls, it was believed that because of its complexity, many bacteria would be required to degrade in nature. By studying the enzymes within this pathway seven brand new enzyme families were discovered, three never before described catalytic activities were characterized, and our understanding of the three-dimensional shape of the sugar was updated. These insights further highlight that investigating the biochemistry of bacteria that live within carbohydrate infused habitats, such as the human intestine, represent a vast repository of potential enzyme for applications for agriculture.
Abstract
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. The metabolism of carbohydrate polymers drives microbial diversity in the human gut microbiota. It is unclear, however, whether bacterial consortia or single organisms are required to depolymerize highly complex glycans. Here we show that the gut bacterium Bacteroides thetaiotaomicron uses the most structurally complex glycan known: The plant pectic polysaccharide rhamnogalacturonan-II, cleaving all but 1 of its 21 distinct glycosidic linkages. The deconstruction of rhamnogalacturonan-II side chains and backbone are coordinated to overcome steric constraints, and the degradation involves previously undiscovered enzyme families and catalytic activities. The degradation system informs revision of the current structural model of rhamnogalacturonan-II and highlights how individual gut bacteria orchestrate manifold enzymes to metabolize the most challenging glycan in the human diet.