Department of Plant Biology, University of Georgia, Athens, GA, 30602, USA.
Department of Chemistry, University of Georgia, Athens, GA, 30602, USA.
Planta. 2018 Jun;247(6):1489-1498. doi: 10.1007/s00425-018-2882-1. Epub 2018 Mar 22.
Rice xylan is predominantly monoacetylated at O-2 and O-3, and 14 rice DUF231 proteins were demonstrated to be xylan acetyltransferases. Acetylated xylans are the principal hemicellulose in the cell walls of grass species. Because xylan acetylation impedes the conversion of cellulosic biomass into biofuels, knowledge on acetyltransferases catalyzing xylan acetylation in grass species will be instrumental for a better utilization of grass biomass for biofuel production. Xylan in rice (Oryza sativa) is predominantly monoacetylated at O-2 and O-3 with a total degree of acetylation of 0.19. In this report, we have characterized 14 rice DUF231 proteins (OsXOAT1 to OsXOAT14) that are phylogenetically grouped together with Arabidopsis xylan acetyltransferases ESK1 and its close homologs. Complementation analysis demonstrated that the expression of OsXOAT1 to OsXOAT7 in the Arabidopsis esk1 mutant was able to rescue its defects in 2-O- and 3-O-monoacetylation and 2,3-di-O-acetylation. Activity assay of recombinant proteins revealed that all 14 OsXOATs exhibited acetyltransferase activities capable of transferring acetyl groups from acetyl-CoA to the xylohexaose acceptor with 10 of them having high activities. Structural analysis of the OsXOAT-catalyzed products showed that the acetylated structural units consisted mainly of 2-O- and 3-O-monoacetylated xylosyl residues with a minor amount of 2,3-di-O-acetylated xylosyl units, which is consistent with the acetyl substitution pattern of rice xylan. Further kinetic studies revealed that OsXOAT1, OsXOAT2, OsXOAT5, OsXOAT6 and OsXOAT7 had high affinity toward the xylohexaose acceptor. Our results provide biochemical evidence indicating that OsXOATs are acetyltransferases involved in xylan acetylation in rice.
水稻木聚糖主要在 O-2 和 O-3 位单乙酰化，14 种水稻 DUF231 蛋白被证明是木聚糖乙酰转移酶。乙酰化木聚糖是禾本科植物细胞壁中主要的半纤维素。由于木聚糖乙酰化会阻碍纤维素生物质转化为生物燃料，因此了解禾本科植物中催化木聚糖乙酰化的乙酰转移酶对于更好地利用草类生物质生产生物燃料具有重要意义。水稻（Oryza sativa）中的木聚糖主要在 O-2 和 O-3 位单乙酰化，乙酰化程度为 0.19。在本报告中，我们对 14 种水稻 DUF231 蛋白（OsXOAT1 至 OsXOAT14）进行了表征，这些蛋白在系统发育上与拟南芥木聚糖乙酰转移酶 ESK1 及其近缘物聚在一起。互补分析表明，在拟南芥 esk1 突变体中表达 OsXOAT1 至 OsXOAT7 能够挽救其在 2-O-和 3-O-单乙酰化以及 2,3-二-O-乙酰化方面的缺陷。重组蛋白的活性测定表明，这 14 种 OsXOAT 都具有将乙酰基从乙酰辅酶 A 转移到木六糖受体上的乙酰转移酶活性，其中 10 种具有高活性。OsXOAT 催化产物的结构分析表明，乙酰化结构单元主要由 2-O-和 3-O-单乙酰化的木糖基残基组成，少量的 2,3-二-O-乙酰化的木糖基单元，这与水稻木聚糖的乙酰化取代模式一致。进一步的动力学研究表明，OsXOAT1、OsXOAT2、OsXOAT5、OsXOAT6 和 OsXOAT7 对木六糖受体具有高亲和力。我们的研究结果提供了生化证据，表明 OsXOAT 是参与水稻木聚糖乙酰化的乙酰转移酶。
