Structure of the Proteus vulgaris HigB-(HigA)2-HigB toxin-antitoxin complex.
Publication Type:Journal Article
Source:J Biol Chem, Volume 289, Issue 2, p.1060-70 (2014)
Keywords:Amino Acid Sequence, Antitoxins, Bacterial Proteins, Catalytic Domain, Crystallography, X-Ray, DNA, Bacterial, Electrophoresis, Polyacrylamide Gel, Models, Molecular, Molecular Sequence Data, Multiprotein Complexes, Nucleic Acid Conformation, Promoter Regions, Genetic, Protein Binding, Protein Multimerization, Protein Structure, Quaternary, Protein Structure, Tertiary, Proteus vulgaris, Repressor Proteins, Ribosomes, Sequence Homology, Amino Acid
<p>Bacterial toxin-antitoxin (TA) systems regulate key cellular processes to promote cell survival during periods of stress. During steady-state cell growth, antitoxins typically interact with their cognate toxins to inhibit activity presumably by preventing substrate recognition. We solved two x-ray crystal structures of the Proteus vulgaris tetrameric HigB-(HigA)2-HigB TA complex and found that, unlike most other TA systems, the antitoxin HigA makes minimal interactions with toxin HigB. HigB adopts a RelE family tertiary fold containing a highly conserved concave surface where we predict its active site is located. HigA does not cover the solvent-exposed HigB active site, suggesting that, in general, toxin inhibition is not solely mediated by active site hindrance by its antitoxin. Each HigA monomer contains a helix-turn-helix motif that binds to its own DNA operator to repress transcription during normal cellular growth. This is distinct from antitoxins belonging to other superfamilies that typically only form DNA-binding motifs upon dimerization. We further show that disruption of the HigB-(HigA)2-HigB tetramer to a HigBA heterodimer ablates operator binding. Taken together, our biochemical and structural studies elucidate the novel molecular details of the HigBA TA system.</p>