Differences in Loop Motions and Dynamics in the Catalytic Domains of GH Family 19 Chitinases Revealed By MD Simulation

Plants produce GH family 19 chitinases as a means of defence against invading fungal pathogens. This family of chitinases has been identified and characterized in a few bacterial species including Streptomyces griseus and Streptomyces coelicolor. Reports have shown that bacterial chitinases require a chitin binding domain for their inhibitory properties against fungi while their plant counterparts in classes I and II of GH family 19, do not require same. Here, we have identified some distinct loop motions in a 20 ns molecular dynamics simulation that suggests that some conformational changes may be triggered by loops in the catalytic domain of plant chitinases which may be essential for recognition and binding to complex or crystalline chitin substrates such as is present in fungal cell walls. In the bacterial chitinases however, the catalytic domain undergoes fewer flexible movements. We propose that such minimal flexibility which might be optimal for binding to chitooligosaccharides as revealed in previous reports, is not sufficient for binding to crystalline chitin. Currently, studies are underway to experiment the influence of redesigning the catalytic domain of Streptomyces griseus chitinase C (ChiC) towards enhancing flexibility in the catalytic domain and subsequently improving its hydrolytic and antifungal properties.