Molecular Mechanism of Polysaccharide Acetylation by the Arabidopsis XylanO-acetyltransferase XOAT1.Lunin, V.V., Wang, H.T., Bharadwaj, V.S., Alahuhta, M., Pena, M.J., Yang, J.Y., Archer-Hartmann, S.A., Azadi, P., Himmel, M.E., Moremen, K.W., York, W.S., Bomble, Y.J., Urbanowicz, B.R.
(2020) Plant Cell 32: 2367-2382
- PubMed: 32354790
- DOI: 10.1105/tpc.20.00028
- Primary Citation of Related Structures:
- PubMed 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 norma ...
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.
Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.