Marine Aspergillus terreus produces a chitinase exhibiting a substrate specific mode of enzymatic action

Marine Aspergillus terreus is explored as an important chitinase-producing fungal strain for N-Acetyl-D-Glucosamine (GlcNAc) production from chitin substrates. Here, a purified extracellular 45 kDa chitinase of marine Aspergillus terreus (accession number JQ248076) was characterized in terms of substrate specificity. Conventionally, endochitinase cleaves chitin randomly to produce GlcNAc and its various multimers. whereas, exochitinases cleave the chitin from its reducing end and produce either GlcNAc or chitobiose (GlcNAc dimer). In the present chitinase characterization, the HPLC followed by HRMS analyses revealed differential product formation from the chitin substrates of varied chain length. With swollen chitin , the enzyme produced GlcNAc as a predominant product; whereas with chitohexaose substrate, a mixture of GlcNAc and its oligomers was obtained. Although mass spectrometry-based proteomics analysis identified the isolated chitinase as an endochitinase 1 precursor (Accession XP_001217186). However, the enzyme kinetic study exhibited higher catalytic efficiency for exochitinase-specific dimeric chromogenic substrate in comparison to endochitinase-specific tetrameric fluorogenic substrate, which indicated predominantly exochitinase behaviour of the enzyme. Further, the in silico study predicted a differential cleavage pattern of the enzyme, which could be due to different mode of substrate binding and processive mechanism through the tunnel-shaped binding cleft of the enzyme. The substrate specificsubstrate specific mode of catalytic activity of present chitinase was further confirmed by a molecular docking study with different lengths of substrates. With unique substrate specific substrate specific mode of action, the chitinase of marine Aspergillus terreus offers a great promise for the production of GlcNAc.