Glycoside hydrolase family 16-Xyloglucan:xyloglucosyl transferases and their roles in plant cell wall structure and mechanics

Abstract

Plant xyloglucan:xyloglucosyl transferases also known as xyloglucan endo-transglycosylases (XETs) are classified in the glycoside hydrolase family 16. This family includes enzymes with a β-jelly-roll fold, which underlies their broad substrate specificity, and the catalytic function to mediate transglycosylation reactions with xyloglucan (XG)-derived or other substrates. This relaxed substrate specificity stems from structural plasticity and plays a fundamental role in plant cell wall re-modeling and mechanics that have evolved to operate in various monophyletic groups. XET enzymes occur in gene families that underlie the synthesis of functional proteins in time- and space-dependent means, and during plant development stresses caused by biotic and ecological stimuli. In this chapter, we focus on XETs and how their singularly carbohydrate-based enzymatic function underlies linking the diverse and complex structures of plant cell walls. We conclude that broad substrate non-specific XETs are plant-prevalent and that these enzymes play roles in targeted cell wall modifications.