Identification of Two Key Enzymes in Xylan Synthesis and Acetylation in Plant Cell Walls
Only a few dozen of the thousands of genes involved plant cell wall biosynthesis have been identified and confirmed. Xylan, a part of hemicellulose, is a major component of plant cell walls and the third most abundant polysaccharide on Earth. The key enzymes responsible for elongation of the xylan backbone and addition of acetyl groups had not been identified, but researchers from the BioEnergy Science Center of Oak Ridge National Laboratory recently identified two key enzymes for the synthesis of this polysaccharide and confirmed their function biochemically. Mutations that impair synthesis of the xylan backbone give rise to plants with collapsed xylem cells and poor growth. Phenotypic analysis of these mutants has implicated many possible proteins in xylan biosynthesis. To further investigate the role of the mutant genes in xylan biosynthesis, recombinant tagged proteins encoded by the Arabidopsis thaliana genes, IRX10-L and ESK1/TBL29, were expressed in vitro and purified. Enzymatic activity of these proteins was inferred from the similarity of their primary amino acid sequence to enzymes of known function. Their enzyme activity was analyzed in vitro by mass spectroscopy and nuclear magnetic resonance. This direct biochemical evidence confirmed the A. thaliana protein IRX10-L enzyme as the xylan synthase and ESK1/TBL29 as the archetypal plant polysaccharide O-acetyltransferase. Thus, two key enzymes for two critical process in xylan (and secondary plant cell wall) synthesis now have been identified, purified, and confirmed. These findings will accelerate understanding of and the ability to manipulate plant cell wall structures for advanced renewable feedstocks for conversion into sugars and fuels or into valuable products such as biomaterials.
Urbanowicz, B. R., M. J. Peña, H. A. Moniz, K. W. Moremen, and W. S. York. 2014. “Two Arabidopsis Proteins Synthesize Acetylated Xylan In Vitro,” The Plant Journal 80(2), 197-206. DOI:10.1111/tpj.12643.