Unraveling the diversity within CAZy families related to hemicellulose degradation

Abstract

Agro-food industrial side streams known as lignocellulosic wastes have received much attention in the last years. These side streams are rich in cellulose, hemicellulose and lignin and can be converted into an array of value-added bioproducts with huge market potentials. Effective bioconversion requires overcoming the recalcitrance of the cell walls of lignocellulosic residues. Hemicellulose is tightly linked to cellulose through hydrogen bonding and to lignin via ester bonds, and its degradation can significantly alter the strength and microstructure of cell walls, thereby improving the overall degradation of agro-food residues. The hydrolysis of hemicellulose requires a variety of fungal enzymes. To date, a considerable number of enzymes have been included into different families in the Carbohydrate Active Enzyme (CAZy) database. However, most of them lack biochemical characterization data, hindering the understanding of diversity within families and the selection of optimal candidates from families for applications. In this thesis, I selectively characterized unknown CAZymes from different CAZy families involved in hemicellulose degradation through fungal genome mining and phylogenetic analysis. Our results discovered novel activities in CAZy families, e.g., feruloyl esterase / acetyl xylan esterase in CE1, xylobiohydrolase in GH30, and endoxyloglucanase in GH44. In addition, I discovered that the expansion of endoxylanases (GH10 and GH11) and α-L-arabinofuranosidase (GH51, GH54, and GH62) in Penicillium subrubescens is followed by functional diversification.