Elucidating the Mechanism of Hemicellulose Biosynthesis: From Genes to Function.

The production of plant biopolymers and functional metabolites requires the coordinated action of numerous enzymes. However, the biochemical function of these biocatalysts and how they work together to synthesize complex biomaterials, like plant cell walls, remains largely unknown. In order to alter or assemble new metabolic pathways, we must first gain a better understanding of these intricate enzymatic systems, which has proven difficult since obtaining plant proteins in pure, active form has been met with limited success. Recently, we have optimized a construct design and heterologously expressed over 40 carbohydrate active enzymes that participate in the biosynthesis of plant cell wall polysaccharides in mammalian cells demonstrating that this is a robust heterologous expression system for these Golgi-resident enzymes. This unprecedented access to large amounts of pure enzymes opens up a new doorway to perform structure-function studies and to investigate complex biochemical pathways in vitro. Now, we have used recombinant plant proteins to synthesize decorated hemicellulosic polymers, resulting in the identification and characterization of the xylan synthase, and the first proof-of-concept generation of enzymatically synthesized, high degree of polymerization (DP), substituted plant polysaccharides in vitro. More recently, this mammalian expression system was to produce large amounts of enzyme required to solve the crystal structure of AtFUT1, a GT37 fucosyltransferase involved in xyloglucan biosynthesis. This represents the first crystal structure of a plant glycosyltransferase involved in cell wall polysaccharide biosynthesis and is a major milestone for the field of plant biochemistry.