The small genetic elements of the toxin-antitoxin are spread in many bacteria, including those that perform photosynthesis: cyanobacteria. In different cells they also have different functions: plasmid stability in the cell, programmed cell death and growth inhibition. Because of them, research into TA systems is also aimed at finding alternatives to antibiotics. Inhibition of cell growth and cell death is caused by a toxin, when it is released from the TA complex. Antitoxin acts as a neutralizing factor in the TA system.
The genome of Microcystis aeruginosa PCC 7806 contains one toxin-antitoxin system next to the orthocaspase MaOC1 transcript, which was found to be responsible for degrading the antitoxin.
It has recently been shown that orthocaspase can cleave an antitoxin, meaning that it could regulate the level of free toxin in the cell. The sites of orthocaspase cleavage on antitoxin have not yet been determined. We expressed and purified the wild-type antitoxin and its three mutated forms. The mutations were at clusters of basic amino acid residues on antitoxin, because MaOC1 prefers to cleave after clusters of basic amino acid residues.
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