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A pair of esterases from a commensal gut bacterium remove acetylations from all positions on complex β-mannans

Michalak, Leszek; Leanti La Rosa, Sabina; Leivers, Shaun Allan; Lindstad, Lars Jordhøy; Kjendseth, Åsmund Røhr; Aachmann, Finn Lillelund; Westereng, Bjørge
Peer reviewed, Journal article
Published version
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Michalak (Locked)
URI
https://hdl.handle.net/11250/2779877
Date
2020
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  • Institutt for bioteknologi og matvitenskap [1172]
  • Publikasjoner fra CRIStin - NTNU [26591]
Original version
Proceedings of the National Academy of Sciences of the United States of America. 2020, 117 (13), 7122-7130.   10.1073/pnas.1915376117
Abstract
β-mannans and xylans are important components of the plant cell wall and they are acetylated to be protected from degradation by glycoside hydrolases. β-mannans are widely present in human and animal diets as fiber from leguminous plants and as thickeners and stabilizers in processed foods. There are many fully characterized acetylxylan esterases (AcXEs); however, the enzymes deacetylating mannans are less understood. Here we present two carbohydrate esterases, RiCE2 and RiCE17, from the Firmicute Roseburia intestinalis, which together deacetylate complex galactoglucomannan (GGM). The three-dimensional (3D) structure of RiCE17 with a mannopentaose in the active site shows that the CBM35 domain of RiCE17 forms a confined complex, where the axially oriented C2-hydroxyl of a mannose residue points toward the Ser41 of the catalytic triad. Cavities on the RiCE17 surface may accept galactosylations at the C6 positions of mannose adjacent to the mannose residue being deacetylated (subsite −1 and +1). In-depth characterization of the two enzymes using time-resolved NMR, high-performance liquid chromatography (HPLC), and mass spectrometry demonstrates that they work in a complementary manner. RiCE17 exclusively removes the axially oriented 2-O-acetylations on any mannose residue in an oligosaccharide, including double acetylated mannoses, while the RiCE2 is active on 3-O-, 4-O-, and 6-O-acetylations. Activity of RiCE2 is dependent on RiCE17 removing 2-O-acetylations from double acetylated mannose. Furthermore, transacetylation of oligosaccharides with the 2-O-specific RiCE17 provided insight into how temperature and pH affects acetyl migration on manno-oligosaccharides.
Publisher
National Academy of Sciences
Journal
Proceedings of the National Academy of Sciences of the United States of America
Copyright
This version of the article will not be available due to copyright restrictions by National Academy of Sciences

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