Solution structures and interaction studies of mycobacterial MazEF6 toxin-antitoxin system

Abstract

Toxin-Antitoxin (TA) systems are stress response systems found on plasmids and chromosomes of bacteria and archaea. They are involved in important functions such as plasmid maintenance, programmed cell death, persister cell formation, phage abortive infection, bacteriostasis and formation of antibiotic -resistant population. The H37Rv strain of Mtb encodes an exceptionally high number ( 90) of TA systems, while the non-pathogenic mycobacterial species, M. smegmatis encodes only 5 TA systems which is relatively fast growing. Majority of the TA systems encoded in the Mtb H37Rv genome are of Type II, MazEF system being a prominent member. The studies have shown that MazE6 and nMazE6 bind to the cognate operator DNA harboring the -10 promoter region (TATACT) with high affinity. The high resolution NMR studies have identified the specific residues neccessary for this binding. Furthermore, it has been shown that the MazE6 does not bind to the non-cognate mazEF9 operator DNA. It has been shown that specificty of interaction lies in the operator DNA sequence as well. Mutation of the operator DNA sequence at the NNN position in TANNNT (TATACT) sequence resulted in weakening of the interaction by 100 fold. Thus, the structures of mycobacterial protein MazE6 and MazF6 from MazEF6 TA complex and function of MazE6 as an antitoxin and as a transcription regulator has been established through this project