title: Structure of the Proteus vulgaris HigB-(HigA)2-HigB toxin-antitoxin complex.
abstract: 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.
authors.affiliation: From the Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Schureck
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Maehigashi
authors.forename: Stacey J
authors.initials: SJ
authors.lastname: Miles
authors.forename: Jhomar
authors.initials: J
authors.lastname: Marquez
authors.forename: Shein Ei
authors.initials: SE
authors.lastname: Cho
authors.forename: Rachel
authors.initials: R
authors.lastname: Erdman
authors.forename: Christine M
authors.initials: CM
authors.lastname: Dunham
mesh_terms: D000595:Amino Acid Sequence; D000992:Antitoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011514:Proteus vulgaris / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D000992:Antitoxins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C587632:HigA protein, Proteus vulgaris; C543139:HigB protein, Proteus vulgaris; D046912:Multiprotein Complexes; D012097:Repressor Proteins
keywords: Bacterial Toxins; Biofilm; Energy Metabolism; Helix-Loop-Helix Transcription Factors; Stress Response; Translation Control; X-ray Crystallography