Purification and characterization of a Bacillus cereus exochitinase

Five extracellular chitinases of Bacillus cereus 6E1 were detected by a novel in-gel chitinase assay using carboxymethyl-chitin-remazol brilliant violet 5R (CM-chitin-RBV) as a substrate. The major chitinase activity was associated with a 36-kDa (Chi36) gel band. Chi36 was purified by a one-step, native gel purification procedure derived from the new in-gel chitinase assay. The purified Chi36 has optimal activity at pH 5.8 and retains some enzymatic activity between pH 2.5-8. The temperature optimum for Chi36 was 35°C, but the enzyme was active between 4-70°C. Based on its ability to hydrolyze mainly p-nitrophenyl-(N-acetyl-β-D-glucosaminide)₂, Chi36 is characterized as a chitobiosidase, a type of exochitinase. The N-terminal amino acid sequence of mature Chi36 was determined (25 amino acids). Alanine is the first N-terminal amino acid residue indicating the cleavage of a signal peptide from a Chi36 precursor to form the mature extracellular Chi36. The N-terminal sequence of Chi36 demonstrated highest similarity with Bacillus circulans WL-12 chitinase D and significant similarity with several other bacterial chitinases.