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- Title
Molecular Mechanism of Polysaccharide Acetylation by the Arabidopsis Xylan O-acetyltransferase XOAT1.
- Authors
Lunin, Vladimir V.; Wang, Hsin-Tzu; Bharadwaj, Vivek S.; Alahuhta, Markus; Peña, Maria J.; Yang, Jeong-Yeh; Archer-Hartmann, Stephanie A.; Azadi, Parastoo; Himmel, Michael E.; Moremen, Kelley W.; York, William S.; 2, Yannick J. Bomble; 2, Breeanna R. Urbanowicz
- Abstract
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 α/β/α 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.
- Publication
Plant Cell, 2020, Vol 32, Issue 7, p2367
- ISSN
1040-4651
- Publication type
Article
- DOI
10.1105/tpc.20.00028