title: Toxin inhibition in C. crescentus VapBC1 is mediated by a flexible pseudo-palindromic protein motif and modulated by DNA binding.
abstract: Expression of bacterial type II toxin-antitoxin (TA) systems is regulated at the transcriptional level through direct binding of the antitoxin to pseudo-palindromic sequences on operator DNA. In this context, the toxin functions as a co-repressor by stimulating DNA binding through direct interaction with the antitoxin. Here, we determine crystal structures of the complete 90 kDa heterooctameric VapBC1 complex from Caulobacter crescentus CB15 both in isolation and bound to its cognate DNA operator sequence at 1.6 and 2.7 Å resolution, respectively. DNA binding is associated with a dramatic architectural rearrangement of conserved TA interactions in which C-terminal extended structures of the antitoxin VapB1 swap positions to interlock the complex in the DNA-bound state. We further show that a pseudo-palindromic protein sequence in the antitoxin is responsible for this interaction and required for binding and inactivation of the VapC1 toxin dimer. Sequence analysis of 4127 orthologous VapB sequences reveals that such palindromic protein sequences are widespread and unique to bacterial and archaeal VapB antitoxins suggesting a general principle governing regulation of VapBC TA systems. Finally, a structure of C-terminally truncated VapB1 bound to VapC1 reveals discrete states of the TA interaction that suggest a structural basis for toxin activation in vivo.
authors.affiliation: Centre for Bacterial Stress Response and Persistence.|Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C, Denmark.
authors.forename: Kirstine L
authors.initials: KL
authors.lastname: Bendtsen
authors.affiliation: Centre for Bacterial Stress Response and Persistence.|Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C, Denmark.
authors.forename: Kehan
authors.initials: K
authors.lastname: Xu
authors.affiliation: Centre for Bacterial Stress Response and Persistence.|Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C, Denmark.
authors.forename: Majbritt
authors.initials: M
authors.lastname: Luckmann
authors.affiliation: Centre for Bacterial Stress Response and Persistence.|Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 København N, Denmark.
authors.forename: Kristoffer S
authors.initials: KS
authors.lastname: Winther
authors.affiliation: Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 København N, Denmark.
authors.forename: Shiraz A
authors.initials: SA
authors.lastname: Shah
authors.affiliation: Bioinformatics Research Centre (BiRC), Aarhus University, C.F. Møllers Allé 8, DK-8000 Aarhus C, Denmark.
authors.forename: Christian N S
authors.initials: CNS
authors.lastname: Pedersen
authors.affiliation: Centre for Bacterial Stress Response and Persistence.|Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C, Denmark.
authors.forename: Ditlev E
authors.initials: DE
authors.lastname: Brodersen
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001427:Bacterial Toxins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D016935:Caulobacter crescentus / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011485:Protein Binding; D000072417:Protein Domains
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; C077517:VapB protein, Bacteria