The Crystal Structure of the Intact E. coli RelBE Toxin-Antitoxin Complex Provides the Structural Basis for Conditional Cooperativity

• Published in: Structure (London) 2012-10, Vol.20 (10), p.1641-1648
• Main Authors: Bøggild, Andreas, Sofos, Nicholas, Andersen, Kasper R., Feddersen, Ane, Easter, Ashley D., Passmore, Lori A., Brodersen, Ditlev E.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacterial Toxins - chemistry; Base Sequence; Crystallography, X-Ray; DNA, Bacterial - chemistry; Escherichia coli; Escherichia coli Proteins - chemistry; Models, Molecular; Molecular Sequence Data; Protein Binding; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Short
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2012.08.017

The bacterial relBE locus encodes a toxin-antitoxin complex in which the toxin, RelE, is capable of cleaving mRNA in the ribosomal A site cotranslationally. The antitoxin, RelB, both binds and inhibits RelE, and regulates transcription through operator binding and conditional cooperativity controlled by RelE. Here, we present the crystal structure of the intact Escherichia coli RelB2E2 complex at 2.8 Å resolution, comprising both the RelB-inhibited RelE and the RelB dimerization domain that binds DNA. RelE and RelB associate into a V-shaped heterotetrameric complex with the ribbon-helix-helix (RHH) dimerization domain at the apex. Our structure supports a model in which relO is optimally bound by two adjacent RelB2E heterotrimeric units, and is not compatible with concomitant binding of two RelB2E2 heterotetramers. The results thus provide a firm basis for understanding the model of conditional cooperativity at the molecular level. ► The E. coli RelB2E2 complex has an open V-shaped structure ► Isolated RelE is conformationally flexible ► The structure is not compatible with two copies binding adjacently on DNA ► The structure suggests a model for conditional cooperativity Bacteria use "self-poisoning" to downregulate cellular processes and to adapt to changing environments. The toxins they use are regulated through tight binding to antitoxins, and Bøggild et al. present the structure of a key intermediate in this subtle regulation mechanism.