Molecular Mechanism of Polysaccharide Acetylation by the Arabidopsis Xylan O-acetyltransferase XOAT1

Vladimir Lunin, Hsin-Tzu Wang, Vivek Bharadwaj, Markus Alahuhta, Maria Pena, Jeong-Yeh Yang, Stephanie Archer-Hartmann, Parastoo Azadi, Michael Himmel, Kelley Moremen, William York, Yannick Bomble, Breeanna Urbanowicz

Research output: Contribution to journalArticlepeer-review

35 Scopus Citations


Xylans are a major component of plant cell walls. O-Acetyl moieties are the dominant backbone substituents of glucuronoxylan in dicots and play a major role in the polymer-polymer interactions that are crucial for wall architecture and normal plant development. Here, we describe the biochemical, structural, and mechanistic characterization of Arabidopsis (Arabidopsis thaliana) xylan O-acetyltransferase 1 (XOAT1), a member of the plant-specific Trichome Birefringence Like (TBL) family. Detailed characterization of XOAT1-catalyzed reactions by real-time NMR confirms that it exclusively catalyzes the 2-O-acetylation of xylan, followed by nonenzymatic acetyl migration to the O-3 position, resulting in products that are monoacetylated at both O-2 and O-3 positions. In addition, we report the crystal structure of the catalytic domain of XOAT1, which adopts a unique conformation that bears some similarities to the a/b/a topology of members of the GDSL-like lipase/acylhydrolase family. Finally, we use a combination of biochemical analyses, mutagenesis, and molecular simulations to show that XOAT1 catalyzes xylan acetylation through formation of an acyl-enzyme intermediate, Ac–Ser-216, by a double displacement bi-bi mechanism involving a Ser-His-Asp catalytic triad and unconventionally uses an Arg residue in the formation of an oxyanion hole.

Original languageAmerican English
Pages (from-to)2367-2382
Number of pages16
JournalPlant Cell
Issue number7
StatePublished - Jul 2020

Bibliographical note

Publisher Copyright:
© 2020 ASPB.

NREL Publication Number

  • NREL/JA-2700-73242


  • acetylation
  • acetyltransferase
  • hemicellulose
  • xylans


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