2h3c
From Proteopedia
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Structural basis for nucleic acid and toxin recognition of the bacterial antitoxin CcdA
Overview
Toxin-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.
About this Structure
2H3C is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
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
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