Gene cloning and characterization of a novel recombinant antifungal chitinase from papaya (carica papaya)

A chitinase cDNA clone (CpCHI, 1002 bp) was isolated from papaya fruit, which encoded a 275 amino acid protein containing a 28 amino acid signal peptide in the N-terminal end. The predicted molecular mass of the mature protein was 26.2 kDa, and its p/value was 6.32. On the basis of its amino acid sequence homology with other plant chitinases, it was classified as a class IV chitinase. An active recombinant CpCHI enzyme was overexpressed in Escherichia coli. The purified recombinant papaya chitinase showed an optimal reaction temperature at 30 °C and a broad optimal pH ranging from 5.0 to 9.0. The recombinant enzyme was quite stable, retaining >64% activity for 3 weeks at 30 °C. The spore germination of Altemaria brassicicola could be completely inhibited by a 76 nM level of recombinant CpCHI. Recombinant CpCHI also showed antibacterial activity in which 50% of £. coli was inhibited by a 2.5 μM concentration of the enzyme.