Comparative analysis of MazEF and HicAB toxin–antitoxin systems of the cyanobacterium,Anabaena sp. PCC7120

Abstract

Anabaena PCC7120 has two annotated toxin-antitoxin systems: MazEF and HicAB. Overexpression of either of the toxins severely inhibited the growth of Escherichia coli BL21(plysS)(DE3). Of the two Anabaena toxins, MazF exhibited higher toxicity than HicA as evidenced by (i) 100-fold lower viability upon overexpression of MazF compared to HicA; (ii) complete loss of cell viability within 1 h of induction of MazF expression, as against >10 colony forming units mL in case of HicA; (iii) inability to maintain the MazF overexpressing plasmid in E. coli cells; and (iv) neutralisation of the toxin was effective at the molar ratio of 1:1.9 for MazF:MazE and 13:1 for HicA:HicB, indicating higher antitoxin requirement for neutralisation of MazF. The growth inhibitory effect of MazF was found to be higher in lag phase cultures compared to mid-logarithmic phase cultures of E. coli, while the reverse was true for HicA. The results suggest possible distinct roles for MazEF and HicAB systems of Anabaena.

The Cysteine Protease MaOC1, a Prokaryotic Caspase Homolog, Cleaves the Antitoxin of a Type II Toxin-Antitoxin System

“…PCC 6803, where several toxins with RNase activity were reported (Ning et al, 2011;Kopfmann et al, 2016;Fei et al, 2018). Two studies were performed with filamentous Anabaena PCC 7120: one characterized the HicAB (Potnis et al, 2017) and the other the MazEF system (Ning et al, 2013). Despite the high number of type II TA systems in M. aeruginosa, none has been characterized experimentally so far.…”