Putative catalytic domain of chitin deacetylase-like proteins from insects and similar proteins
Chitin deacetylases (CDAs, EC 3.5.1.41) are secreted metalloproteins belonging to a family of extracellular chitin-modifying enzymes that catalyze the N-deacetylation of chitin, a beta-1,4-linked N-acetylglucosamine polymer, to form chitosan, a polymer of beta-(1,4)-linked d-glucosamine residues. CDAs have been isolated and characterized from various bacterial and fungal species and belong to the larger carbohydrate esterase family 4 (CE4). This family includes many CDA-like proteins, mainly from insects, which contain a putative CDA-like catalytic domain similar to the catalytic NodB homology domain of CE4 esterases. Some family members have an additional chitin binding domain (ChBD), or an additional low-density lipoprotein receptor class A domain (LDLa), or both. Due to the lack of some catalytically relevant residues, several insect CDA-like proteins are devoid of enzymatic activity and may simply bind to chitin and thus influence the mechanical or permeability properties of chitin-containing structures such as the cuticle or the peritrophic membrane. This family also includes many uncharacterized hypothetical proteins from bacteria, exhibiting high sequence similarity to insect CDA-like proteins.
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