3o6q
The Structure of SpoIISA and SpoIISB, a Toxin - Antitoxin System
Structural highlights
FunctionSP2SA_BACSU Toxic component of a toxin-antitoxin (TA) module. Its toxic activity is neutralized by cognate antitoxin SpoIISB. Expression in the absence of SpoIISB permits sporulation to stage II, when plasmolysis zones and holes in the peptidoglycan layer are observed, resulting in cell death. Lethal when synthesized during vegetative growth in the absence of SpoIISB. In E.coli both the membrane bound and soluble domain are required in cis for toxin activity.[1] Publication Abstract from PubMedSpore formation in Bacillus subtilis begins with an asymmetric cell division following which differential gene expression is established by alternative compartment-specific RNA polymerase sigma factors. The spoIISAB operon of B. subtilis was identified as a locus whose mutation leads to increased activity of the first sporulation-specific sigma factor, SigF. Inappropriate spoIISA expression causes lysis of vegetatively growing B. subtilis cells and E. coli cells when expressed heterologously, effects that are countered by co-expression of spoIISB, identifying SpoIISA-SpoIISB as a toxin-antitoxin system. SpoIISA has three putative membrane-spanning segments and a cytoplasmic domain. Here, the crystal structure of a cytoplasmic fragment of SpoIISA (CSpoIISA) in complex with SpoIISB has been determined by SeMet-MAD phasing to 2.5 A spacing revealing a CSpoIISA2: SpoIISB2 heterotetramer. CSpoIISA has a single domain alpha-beta structure resembling a GAF domain with an extended alpha-helix at its amino terminus. The two CSpoIISA protomers form extensive interactions through an intermolecular 4-helix bundle. Each SpoIISB chain is highly extended and lacking tertiary structure. The SpoIISB chains wrap around the CSpoIISA dimer forming extensive interactions with both CSpoIISA protomers. CD spectroscopy experiments indicate that SpoIISB is a natively disordered protein that adopts structure only in the presence of CSpoIISA while surface plasmon resonance experiments revealed that the CSpoIISA: SpoIISB complex is stable with a dissociation constant in the nanomolar range. The results are interpreted in relation to sequence conservation and mutational data and possible mechanisms of cell killing by SpoIISA are discussed. The structure and interactions of SpoIISA and SpoIISB, a toxin-antitoxin system in Bacillus subtilis.,Florek P, Levdikov VM, Blagova E, Lebedev AA, Skrabana R, Resetarova S, Pavelcikova P, Barak I, Wilkinson AJ J Biol Chem. 2010 Dec 7. PMID:21147767[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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