2h3c
Structural basis for nucleic acid and toxin recognition of the bacterial antitoxin CcdA
Structural highlights
FunctionCCDA_ECOLI Antitoxin component of a toxin-antitoxin (TA) module which inhibits the post-segregational killing (PSK) of plasmid-free cells, also referred to as a plasmid addiction system. Labile antitoxin with a half-life of about 1 hour in the presence of CcdB. Binds to and blocks the activity of CcdB; will also remove bound CcdB protein from the CcdB-GyrA complex by forming a CcdA-CcdB complex, a process termed rejuvenation. The N-terminal 36 residues are not required for rejuventation. Functions as a transcriptional corepressor for the ccdAB operon, repression also requires CcdB.[1] [2] [3] [4] [5] [6] [7] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedToxin-antitoxin systems are highly abundant in plasmids and bacterial chromosomes. They ensure plasmid maintenance by killing bacteria that have lost the plasmid. Their expression is autoregulated at the level of transcription. Here, we present the solution structure of CcdA, the antitoxin of the ccd system, as a free protein (16.7 kDa) and in complex with its cognate DNA (25.3 kDa). CcdA is composed of two distinct and independent domains: the N-terminal domain, responsible for DNA binding, which establishes a new family of the ribbon-helix-helix fold and the C-terminal region, which is responsible for the interaction with the toxin CcdB. The C-terminal domain is intrinsically unstructured and forms a tight complex with the toxin. We show that CcdA specifically recognizes a 6 bp palindromic DNA sequence within the operator-promoter (OP) region of the ccd operon and binds to DNA by insertion of the positively charged N-terminal beta-sheet into the major groove. The binding of up to three CcdA dimers to a 33mer DNA of its operator-promoter region was studied by NMR spectroscopy, isothermal titration calorimetry and single point mutation. The highly flexible C-terminal region of free CcdA explains its susceptibility to proteolysis by the Lon ATP-dependent protease. Structural basis for nucleic acid and toxin recognition of the bacterial antitoxin CcdA.,Madl T, Van Melderen L, Mine N, Respondek M, Oberer M, Keller W, Khatai L, Zangger K J Mol Biol. 2006 Nov 24;364(2):170-85. Epub 2006 Sep 1. PMID:17007877[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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