Mycobacterium susceptibility to ivermectin by inhibition of eccD3, an ESX-3 secretion system component

Drug-resistant tuberculosis is a pressing global health issue that requires the development of new drugs or the identification of new therapeutic targets. The ESX-3 secretion system is essential for the Mycobacterium tuberculosis growth and plays a role in iron/zinc homeostasis and virulence. The aim of this study was to evaluate the quaternary interface of EccD3, a component of the ESX-3 secretion system, and to evaluate the association of an eccD3 mutant with drug resistance. The molecular structures of EccD3 protein and other ESX-3 secretion system proteins of the M. tuberculosis were predicted based in homology with the Mycolicibacterium smegmatis tertiary protein structures. According to the in silico results, selamectin, avermectin, ivermectin, and moxidectin were selected as prospective drugs. Selamectin and moxidectin had favorable ΔG values for the EccB3 and EccD3 dimer interfaces, whereas the ESX-3 Protomer 1 interface had the best ΔG + with avermectin, ivermectin, and moxidectin. Furthermore, ivermectin susceptibility increased when the eccD3 gene was inhibited using CRISPRi in M. smegmatis. Blockage of EccD3 increased the ivermectin action, but the modest changes observed may be explained by the compensatory mechanisms or other ivermectin targets in absence of this Esx3 component. Further in vitro and preclinical studies are required to validate our findings.