Heterologous expression of the antifungal β-chitin binding protein CBP24 from bacillus thuringiensis and its synergistic action with bacterial chitinases.

Abstract

The genome sequence analysis of Bacillus thuringiensis serovar konkukian S4 has shown to contain two chitinases (Chi74, Chi39) and two chitin-binding proteins (CBP50 and CBP24). The Chi74, Chi39 and CBP50 have been characterized previously. The chitin-binding protein CBP24 was cloned and heterologously expressed in Escherichia coli. The recombinant protein was purified using a Ni-NTA purification system. The purified protein was used to study its substrate binding activity using crystalline chitin variants as substrates. The Bmax and Kd values have shown that it preferably binds to β-type of the crystalline chitin at a range of pH with peak activity between 5.5-7.5. To elucidate the role of CBP24 in the chitin degradation system of S4, the purified chitinases Chi74, Chi39 along with the ChiA from Serratia proteamcualans were used in different combinations with the CBP24 and chitinolytic activity was assayed. It was shown that the CBP24 acts synergistically with chitin degradation activity of bacterial chitinases non-specifically. Moreover, the CBP24 has shown antifungal activity against plant pathogenic fungi Fusarium oxysporum and Rhizoctonia solani. The present study will lead us to develop a technology for environmental friendly conversion of chitin to valuable products.