Implication on the Function of Novel Xn-relE Toxin Structure of Xenorhabdus nematophila Using Homology Modeling

Background: Bacterial chromosomal toxin-antitoxin systems are involved in various cell functions such as stress response, promoting cell cycle arrest and bringing about the onset of programmed cell death. Unlike RelBE TA module of Escherichia coli, genome of Xenorhabdus nematophila has two separate TA modules for RelB and RelE. Here RelE being the toxin bears its own antitoxin and RelB antitoxin bears its separate toxin counterpart. More interestingly these modules are located distantly in genome. Objective: In this study, Xn-relE toxin model structure from X. nematophila is explored for the first time. Toxic effect of Xn-relE has already been shown by endogenous killing in our earlier report. Methods: Since no crystallographic structure for Xn-relE toxin is available till date. The models of X. nematophila Xn-relE toxin and its antitoxin Xn-relEAT were developed using the I-TASSER server and analyzed to define gene ontology. The models were validated by using VERIFY-3D. Results: Homology models for X. nematophila Xn-relE toxin and its antitoxin Xn-relEAT was obtained and interactions were established. The structural and functional annotation of this TA system designate it as Type II TA module. Conclusion: The present study sheds light on the structure and function of Xn-relE toxin of Xn RelE TA module, whose applicability in the area of agricultural sciences is pronounced.