Carboxy-terminal glycosyl hydrolase 18 domain of a carbohydrate active protein of Chitinophaga pinensis is a non-processive exochitinase.

The recombinant C-terminal domain of chitinase C of Chitinophaga pinensis (CpChiC-GH18) exhibits the highest activity at pH 6.0 and 35 °C, with a K of 76.13 (mg ml), a k of 10.16 (s), and a k/K of 0.133 (mg ml s) on colloidal chitin. Analysis of degradation of (GlcNAc) oligomers shows that CpChiC-GH18 releases (GlcNAc) as the main product, indicating an exo-type cleavage pattern. CpChiC-GH18 hydrolyzes the chitin polymers yielding GlcNAc, (GlcNAc), and (GlcNAc) as end products with no sign of processivity. Circular dichroism spectra indicate that the secondary and tertiary structures of CpChiC-GH18 are unaltered up to 45 °C and the protein denatures without an intermediate state. The urea-induced unfolding is a two-state process and the unfolding of native CpChiC-GH18 occurs in a single step. Among the metal ions tested, Hg completely inhibits the enzyme activity. The chemical modulators, p-hydroxymercuribenzoic acid and N-bromosuccinimide considerably decrease the enzyme activity. Sequence analysis and homology modeling suggest that CpChiC-GH18 lacks a tryptophan residue at the aglycon site. Further, the CpChiC-GH18 has a shallow and open groove, suggesting that CpChiC-GH18 is non-processive exo-type chitinase with properties suitable for the bioconversion of chitin waste.