ABSTRACT
The matrix of polysaccharides presents a great structural diversity in the plant cell wall. Each molecule may contain different sugar residues with the same or different bonds, branched to varying degrees. The term holocellulose is used to describe a diverse group of polysaccharides, including cellulose and hemicelluloses that occur in close association with lignin (Andreaus et al. 2008, Khandeparker and Numan 2008). The presence of enzymes that break the various branch points is essential for complete hydrolysis of the plant cell wall holocellulose structure, creating more sites for subsequent enzymatic hydrolysis. They may also have a role in the introduction of specifi c modifi cations in the polysaccharide structure, such as changing solubility, polymer confi guration and linkages to phenolic compounds and lignin. Within this context, α-glucuronidases are key enzymes in the cleavage
Enzymology Laboratory, Cellular Biology Department, University of Brasília, Brasilia, 70910900, Federal District, Brazil. *Corresponding author: eximenes@unb.br
of glucuronic acid side-groups that protect the neighboring β-1,4-linkages of the xylan backbone from being cleaved by xylan-degrading enzymes (Biely et al. 2000, Nagy et al. 2002, de Wet et al. 2006).
