ABSTRACT
Chitinases which degrade chitin have attracted attention as biological antifungal agents. The purpose of this study is to isolate Streptomyces from Fadama soil and assess its chitinolytic and antagonist potential against phytopathogenic fungi for application as biocontrol agent. Streptomyces were isolated from Fadama soil. The selected isolate CT02 exhibited chitinolytic characteristics. Chitinase production was performed under different temperatures, pH and varying incubation period. The highest chitinase production by CT02 isolate was observed after five days of cultivation. The highest chitinase activity was observed at 35°C and pH 7. The crude extracellular enzyme exhibited a specific activity of 4.20 U/µg whereas partially purified extracellular enzyme exhibited a specific activity of 6.19 U/µg with purification fold of 1.47. The selected isolate CT02 and its extracellular crude chitinase showed in vitro antifungal antagonist potential by inhibiting the growth of Aspergillus niger and Aspergillus oryzae. This indicates that Streptomyces derived chitinases are potential biocontrol agents against phytopathogenic fungi.
ABSTRACT
BACKGROUND: Human Exonuclease1 (hExo1) participates in the resection of DNA double-strand breaks by generating long 3'-single-stranded DNA overhangs, critical for homology-based DNA repair and activation of the ATR-dependent checkpoint. The C-terminal region is essential for modulating the activity of hExo1, containing numerous sites of post-translational modification and binding sites for partner proteins. METHODS: Analytical Ultracentrifugation (AUC), Dynamic Light Scattering (DLS), Circular Dichroism (CD) spectroscopy and enzymatic assays. RESULTS: AUC and DLS indicates the C-terminal region has a highly extended structure while CD suggest a tendency to adopt a novel left-handed ß-sheet structure, together implying the C-terminus may exhibit a transient fluctuating structure that could play a role in binding partner proteins known to regulate the activity of hExo1. Interaction with 14-3-3 protein has a cooperative inhibitory effect upon DNA resection activity, which indicates an allosteric transition occurs upon binding partner proteins. CONCLUSIONS: This study has uncovered that hExo1 consist of a folded N-terminal nuclease domain and a highly extended C-terminal region which is known to interact with partner proteins that regulates the activity of hExo1. A positively cooperative mechanism of binding allows for stringent control of hExo1 activity. Such a transition would coordinate the control of hExo1 by hExo1 regulators and hence allow careful coordination of the process of DNA end resection. SIGNIFICANCE: The assays presented herein could be readily adapted to rapidly identify and characterise the effects of modulators of the interaction between the 14-3-3 proteins and hExo1. It is conceivable that small molecule modulators of 14-3-3 s-hExo1 interaction may serve as effective chemosensitizers for cancer therapy.
