A novel membrane bound toxin for cell division CptA (YgfX) inhibits polymerization of cytoskeleton proteins FtsZ and MreB in Escherichia coli

摘要

Nearly all free living bacteria carry toxin-antitoxin (TA) systems on their genomes, through which cell growth and death are regulated. Toxins target a variety of essential cellular functions, including DNA replication, translation, and cell division. Here we identified a novel toxin, YgfX, on the E. coli genome. The toxin, consisting of 135 residues, is composed of the N-terminal membrane domain, which encompasses two transmembrane segments, and the C-terminal cytoplasmic domain. Upon YgfX expression, the cells were initially elongated and then the middle portion of the cells became inflated to form a lemon-shape. YgfX was found to interact with MreB and FtsZ, two essential cytoskeletal proteins in E. coli. The cytoplasmic domain [YgfX(C)], was found to be responsible for the YgfX toxicity, as purified YgfX(C) was found to block polymerization of FtsZ and MreB in vitro. YgfY, located immediately upstream of YgfX, was shown to be the cognate antitoxin. Notably, YgfX is the first membrane associating toxin in bacterial TA systems. We propose to rename the toxin and the antitoxin as CptA and CptB (for >Cytoskeleton >Polymerization inhibiting >Toxin), respectively.