2xd0 | pdb_00002xd0
A processed non-coding RNA regulates a bacterial antiviral system
Structural highlights
FunctionTOXN_PECAT Toxic component of a type III toxin-antitoxin (TA) system. An endoribonuclease which is active independently of the ribosome, cleaving between the second and third A of AAA(U/G) sequences, although not all occurrences of this tetranucleotide are cleaved (PubMed:23267117). Digests many mRNA species, including its own transcript and its cognate antitoxin RNA ToxI. ToxI has 5.5 nearly identical 36 nucleotide-long repeats (a single repeat neutralizes the toxin in vivo); a single repeat folds into a pseudoknot which binds the toxin (PubMed:21240270). The ToxI precursor RNA is a preferential target in vivo and is progressively degraded to single repeat lengths as ToxN-ToxI complex self-assembly occurs (PubMed:23267117). In vivo expression of ToxI antitoxin inhibits endonuclease activity of ToxN (PubMed:23267117). The toxin alone inhibits growth when expressed in E.coli without causing cell lysis; this bacteriostatic effect is neutralized by cognate RNA antitoxin ToxI (PubMed:19124776, PubMed:23267117). Non-cognate antitoxin RNA from B.thuringiensis does not inhibit this toxin (PubMed:23267117). The RNA antitoxin is less stable than the proteinaceous toxin; synthesis of ToxI in the absence of new ToxN synthesis restores growth and also detectable accumulation of the ToxN protein (PubMed:19124776). Negatively regulates its own operon in complex with ToxI (PubMed:19633081). The toxin-antitoxin system functions in plasmid maintenance (a plasmid addiction system) (PubMed:23267117).[1] [2] [3] [4] The TA system protects P.atrosepticum strain 1043 against phage phiM1 and phiA2, E.coli against some but not all coliphages and S.marcescens against some bacteriophages, causing an abortive infection (Abi phenotype) (PubMed:19124776). Also protects P.atrosepticum strain 1043 against phage phiTE; phage that escape Abi and grow in this bacterium have evolved a pseudo-ToxI RNA by expanding a pre-existing sequence similar to the bona fide ToxI repeats (PubMed:23109916).[5] [6] Publication Abstract from PubMedThe >/=10(30) bacteriophages on Earth relentlessly drive adaptive coevolution, forcing the generation of protective mechanisms in their bacterial hosts. One such bacterial phage-resistance system, ToxIN, consists of a protein toxin (ToxN) that is inhibited in vivo by a specific RNA antitoxin (ToxI); however, the mechanisms for this toxicity and inhibition have not been defined. Here we present the crystal structure of the ToxN-ToxI complex from Pectobacterium atrosepticum, determined to 2.75-A resolution. ToxI is a 36-nucleotide noncoding RNA pseudoknot, and three ToxI monomers bind to three ToxN monomers to generate a trimeric ToxN-ToxI complex. Assembly of this complex is mediated entirely through extensive RNA-protein interactions. Furthermore, a 2'-3' cyclic phosphate at the 3' end of ToxI, and catalytic residues, identify ToxN as an endoRNase that processes ToxI from a repetitive precursor but is regulated by its own catalytic product. A processed noncoding RNA regulates an altruistic bacterial antiviral system.,Blower TR, Pei XY, Short FL, Fineran PC, Humphreys DP, Luisi BF, Salmond GP Nat Struct Mol Biol. 2011 Feb;18(2):185-90. Epub 2011 Jan 16. PMID:21240270[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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