6cci
The Crystal Structure of XOAT1
Structural highlights
FunctionTBL29_ARATH Probable xylan acetyltransferase required for 2-O- and 3-O-monoacetylation of xylosyl residues in xylan. Negative regulator of cold acclimation. Involved in water economy as well as salt tolerance. Regulated at the transcriptional level by NAC012/SND1 (PubMed:17316173, PubMed:19054354, PubMed:19061521, PubMed:21408051, PubMed:23340742, PubMed:23659919). May act as a bridging protein that binds pectin and other cell wall polysaccharides. Probably involved in maintaining esterification of pectins (By similarity).[UniProtKB:Q9FG35][1] [2] [3] [4] [5] [6] Publication Abstract from PubMedXylans 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 alpha/beta/alpha 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. Molecular Mechanism of Polysaccharide Acetylation by the Arabidopsis Xylan O-acetyltransferase XOAT1.,Lunin VV, Wang HT, Bharadwaj VS, Alahuhta M, Pena MJ, Yang JY, Archer-Hartmann SA, Azadi P, Himmel ME, Moremen KW, York WS, Bomble YJ, Urbanowicz BR Plant Cell. 2020 Jul;32(7):2367-2382. doi: 10.1105/tpc.20.00028. Epub 2020 Apr, 30. PMID:32354790[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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