Complex Carbohydrate Research Center - University of Georgia

__________

Host:  Olga Zabotina

__________

"Hemicellulose Biosynthesis:  From Genes to Function"

Enzymes capable of catalyzing the entire spectrum of possible glycosidic linkages currently known to exist in plants still await discovery. Understanding the identity, selectivity, and catalytic mechanisms of plant biocatalysts involved in wall formation is paramount to unravelling the roles these enzymes play in generating structures critical to wall architecture. However, the biochemical function of these biocatalysts and how they work together to synthesize complex biopolymers remains largely unknown.

Much of my recent research has focused on the hemicellulosic polysaccharides xylan and xyloglucan as models to study plant glycopolymer biosynthesis, resulting in the identification and biochemical characterization of several of the enzymes in the xylan biosynthesis pathway, including Xylan Synthase-1 (XYS1), Glucuronoxylan Methytransferase 1 (GXMT1) and Xylan O-Acetyltransferase 1 (XOAT1). I have shown that these enzymes can be reacted in different combinations, resulting in the first proof-of-concept generation of enzymatically synthesized, high degree of polymerization (DP), substituted plant polysaccharides in vitro. This has facilitated the development of a robust model system to study complex polymer biosynthesis.

Recently, we have been taking a multidisciplinary approach to study the mechanistic underpinnings of the enzymes involved in plant cell wall biosynthesis. Recently, we solved the structure of XOAT1, which represents the first crystal structure of an enzyme involved in both plant polysaccharide acetylation and in xylan biosynthesis. We elucidate its structure using X-ray crystallography, provide molecular level insights into the active site dynamics and substrate binding modes using molecular simulations and finally present and validate a viable mechanism for xylan acetylation using mutagenesis experiments.