Endo-1,4-8-xylanase-containing glycoside hydrolase families: characteristics, singularities and similarities

Endo-1,4-8-xylanases (EC 3.2.1.8) are O-glycoside hydrolases that cleave the internal 8-1,4-D-xylosidic linkages of the complex plant polysaccharide xylan. They are produced by a vast array of organisms where they play critical roles in xylan saccharification and plant cell wall hydrolysis. They are also important industrial bio-catalysts with widespread application. A large and ever growing number of xylanases with wildly different properties and functionalites are known and a better understanding of these would enable a more effective use in various applications. The Carbohydrate-Active enZYmes database (CAZy), which classifies evolutionarily related proteins into a glycoside hydrolase family-subfamily organisational scheme has proven powerful in under-standing these enzymes. Nevertheless, ambiguity currently exists as to the number of glycoside hydrolase fam-ilies and subfamilies harbouring catalytic domains with true endoxylanase activity and as to the specific characteristics of each of these families/subfamilies. This review seeks to clarify this, identifying 9 glycoside hydrolase families containing enzymes with endo-1,4-8-xylanase activity and discussing their properties, simi-larities, differences and biotechnological perspectives. In particular, substrate specificities and hydrolysis pat-terns and the structural determinants of these are detailed, with taxonomic aspects of source organisms being also presented. Shortcomings in current knowledge and research areas that require further clarification are highlighted and suggestions for future directions provided. This review seeks to motivate further research on these enzymes and especially of the lesser known endo-1,4-8-xylanase containing families. A better under-standing of these enzymes will serve as a foundation for the knowledge-based development of process-fitted endo-1,4-8-xylanases and will accelerate their development for use with even the most recalcitrant of sub-strates in the biobased industries of the future.

Automated summary

This article summarizes 9 glycoside hydrolase families containing enzymes with endo-1,4-8-xylanase activity and discusses their properties, similarities, differences, and biotechnological perspectives. It provides detailed information on substrate specificities, hydrolysis patterns, and the structural determinants of these enzymes, as well as taxonomic aspects of the source organisms. The article highlights shortcomings in current knowledge and identifies research areas that require further clarification. It aims to motivate further research on these enzymes and particularly on the lesser-known endo-1,4-8-xylanase containing families, which will serve as a foundation for the knowledge-based development of process-fitted enzymes in the biobased industries of the future.