Current perspectives on the families of glycoside hydrolases of Mycobacterium tuberculosis: their importance and prospects for assigning function to unknowns

Glycoside hydrolases (GHs) are enzymes that catalyze the hydrolysis of glycosidic bonds in glycoconjugates, oligo- and polysaccharides. A classification of these enzymes based on conserved sequence and structure motifs supported by the Carbohydrate Active Enzyme (CAZy) database has proven useful in the systematic groupings of similar enzymes into families. The human pathogen Mycobacterium tuberculosis employs 30 GHs to perform a variety of different functions, which can be divided into four broad categories: α-glucan metabolism, peptidoglycan remodeling, β-glycan hydrolysis and α-demannosylation. The review presented here shows how the GHs that have been characterized play a role in each category. Expanding the genomic analysis of GH presence to other Mycobacterium species has highlighted the importance of certain families-most notably GH13 and GH23-in the general genomic make-up of mycobacteria. Since many GHs are still uncharacterized and considered as "conserved hypothetical" proteins, the grouping of them into respective families provides a strong prediction on their putative biological functions.