Catalytic NodB homology domain of Colletotrichum lindemuthianum chitin deacetylase and similar proteins. This family is represented by the chitin deacetylase (endo-chitin de-N-acetylase, ClCDA, EC 3.5.1.41) from Colletotrichum lindemuthianum (also known as Glomerella lindemuthiana), which is a member of the carbohydrate esterase 4 (CE4) superfamily. ClCDA catalyzes the hydrolysis of N-acetamido groups of N-acetyl-D-glucosamine residues in chitin, converting it to chitosan in fungal cell walls. It consists of a single catalytic domain similar to the deformed (alpha/beta)8 barrel fold adopted by other CE4 esterases, which encompasses a mononuclear metalloenzyme employing a conserved His-His-Asp zinc-binding triad closely associated with the conserved catalytic base (aspartic acid) and acid (histidine), to carry out acid/base catalysis. It possesses a highly conserved substrate-binding groove, with subtle alterations that influence substrate specificity and subsite affinity. Unlike its bacterial homologs, ClCDA contains two intramolecular disulfide bonds that may add stability to this secreted protein. The family also includes many uncharacterized deacetylases and hypothetical proteins mainly from eukaryotes, which show high sequence similarity to ClCDA.

Catalytic NodB homology domain of uncharacterized bacterial polysaccharide deacetylases. This family includes many uncharacterized bacterial polysaccharide deacetylases. Although their biological function still remains unknown, members in this family show high sequence homology to the catalytic NodB homology domain of Streptococcus pneumoniae polysaccharide deacetylase PgdA (SpPgdA), which is an extracellular metal-dependent polysaccharide deacetylase with de-N-acetylase activity toward a hexamer of chitooligosaccharide N-acetylglucosamine, but not shorter chitooligosaccharides or a synthetic peptidoglycan tetrasaccharide. Like SpPgdA, this family is a member of the carbohydrate esterase 4 (CE4) superfamily.

Catalytic NodB homology domain of uncharacterized bacterial glycosyl transferase, group 2-like family proteins. This family includes many uncharacterized bacterial proteins containing an N-terminal GH18 (glycosyl hydrolase, family 18) domain, a middle NodB-like homology domain, and a C-terminal GT2-like (glycosyl transferase group 2) domain. Although their biological function is unknown, members in this family contain a middle NodB homology domain that is similar to the catalytic domain of Streptococcus pneumoniae polysaccharide deacetylase PgdA (SpPgdA), an extracellular metal-dependent polysaccharide deacetylase with de-N-acetylase activity toward a hexamer of chitooligosaccharide N-acetylglucosamine, but not shorter chitooligosaccharides or a synthetic peptidoglycan tetrasaccharide. Like SpPgdA, this family is a member of the carbohydrate esterase 4 (CE4) superfamily. The presence of three domains suggests that members of this family may be multifunctional.

Catalytic NodB homology domain of Streptococcus mutans polysaccharide deacetylase PgdA, Bacillus subtilis YheN, and similar proteins. This family is represented by a putative polysaccharide deacetylase PgdA from the oral pathogen Streptococcus mutans (SmPgdA) and Bacillus subtilis YheN (BsYheN), which are members of the carbohydrate esterase 4 (CE4) superfamily. SmPgdA is an extracellular metal-dependent polysaccharide deacetylase with a typical CE4 fold, with metal bound to a His-His-Asp triad. It possesses de-N-acetylase activity toward a hexamer of chitooligosaccharide N-acetylglucosamine, but not shorter chitooligosaccharides or a synthetic peptidoglycan tetrasaccharide. SmPgdA plays a role in tuning cell surface properties and in interactions with (salivary) agglutinin, an essential component of the innate immune system, most likely through deacetylation of an as-yet-unidentified polysaccharide. SmPgdA shows significant homology to the catalytic domains of peptidoglycan deacetylases from Streptococcus pneumoniae (SpPgdA) and Listeria monocytogenes (LmPgdA), both of which are involved in the bacterial defense mechanism against human mucosal lysozyme. The Bacillus subtilis genome contains six polysaccharide deacetylase gene homologs: pdaA, pdaB (previously known as ybaN), yheN, yjeA, yxkH and ylxY. The biological function of BsYheN is still unknown. This family also includes many uncharacterized polysaccharide deacetylases mainly found in bacteria.

Catalytic NodB homology domain of rhizobial NodB-like proteins. This family belongs to the large and functionally diverse carbohydrate esterase 4 (CE4) superfamily, whose members show strong sequence similarity with some variability due to their distinct carbohydrate substrates. It includes many rhizobial NodB chitooligosaccharide N-deacetylase (EC 3.5.1.-)-like proteins, mainly from bacteria and eukaryotes, such as chitin deacetylases (EC 3.5.1.41), bacterial peptidoglycan N-acetylglucosamine deacetylases (EC 3.5.1.-), and acetylxylan esterases (EC 3.1.1.72), which catalyze the N- or O-deacetylation of substrates such as acetylated chitin, peptidoglycan, and acetylated xylan. All members of this family contain a catalytic NodB homology domain with the same overall topology and a deformed (beta/alpha)8 barrel fold with 6- or 7 strands. Their catalytic activity is dependent on the presence of a divalent cation, preferably cobalt or zinc, and they employ a conserved His-His-Asp zinc-binding triad closely associated with the conserved catalytic base (aspartic acid) and acid (histidine) to carry out acid/base catalysis. Several family members show diversity both in metal ion specificities and in the residues that coordinate the metal.