4ato
New insights into the mechanism of bacterial Type III toxin-antitoxin systems: selective toxin inhibition by a non-coding RNA pseudoknot
Structural highlights
FunctionTOXN_BACTK Toxic component of a type III toxin-antitoxin (TA) system (PubMed:19124776). An endoribonuclease which cleaves between the first and second A of AAAAA sequences; it tolerates other nucleotides in positions +2 and +4 of the consensus. Digests cognate antitoxin RNA ToxI as shown by the 2'-3'-cyclic phosphate at the 3' end of the 34-nt repeats and probably other RNAs (PubMed:23267117). Inhibits growth when expressed in E.coli without causing cell lysis; this bacteriostatic effect is neutralized by cognate RNA antitoxin ToxI, which has 2.9 nearly identical 34 nucleotide-long repeats (PubMed:19124776). Non-cognate antitoxin RNA from P.atrosepticum does not inhibit this toxin (PubMed:23267117). The toxin-antitoxin pair function in plasmid maintenance (a plasmid addiction system), but unlike its P.atrosepticum homolog it is not seen to confer resistance to bacteriophages (PubMed:23267117).[1] [2] Publication Abstract from PubMedBacterial small RNAs perform numerous regulatory roles, including acting as antitoxic components in toxin-antitoxin systems. In type III toxin-antitoxin systems, small processed RNAs directly antagonize their toxin protein partners, and in the systems characterized the toxin and antitoxin components together form a trimeric assembly. In the present study, we sought to define how the RNA antitoxin, ToxI, inhibits its potentially lethal protein partner, ToxN. We show through cross-inhibition experiments with the ToxIN systems from Pectobacterium atrosepticum (ToxIN(Pa)) and Bacillus thuringiensis (ToxIN(Bt)) that ToxI RNAs are highly selective enzyme inhibitors. Both systems have an "addictive" plasmid maintenance phenotype. We demonstrate that ToxI(Pa) can inhibit ToxN(Pa) in vitro both in its processed form and as a repetitive precursor RNA, and this inhibition is linked to the self-assembly of the trimeric complex. Inhibition and self-assembly are both mediated entirely by the ToxI(Pa) RNA, with no requirement for cellular factors or exogenous energy. Finally, we explain the origins of ToxI antitoxin selectivity through our crystal structure of the ToxIN(Bt) complex. Our results show how a processed RNA pseudoknot can inhibit a deleterious protein with exquisite molecular specificity and how these self-contained and addictive RNA-protein pairs can confer different adaptive benefits in their bacterial hosts. Selectivity and self-assembly in the control of a bacterial toxin by an antitoxic noncoding RNA pseudoknot.,Short FL, Pei XY, Blower TR, Ong SL, Fineran PC, Luisi BF, Salmond GP Proc Natl Acad Sci U S A. 2012 Dec 24. PMID:23267117[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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