ID   CCDB2_ECOLX             Reviewed;         101 AA.
AC   Q46996;
DT   01-NOV-1997, integrated into UniProtKB/Swiss-Prot.
DT   01-NOV-1997, sequence version 1.
DT   25-MAY-2022, entry version 68.
DE   RecName: Full=Toxin CcdB;
DE   AltName: Full=Cytotoxic protein CcdB;
DE   AltName: Full=Protein LetD;
GN   Name=ccdB; Synonyms=letB;
OS   Escherichia coli.
OG   Plasmid TP181.
OC   Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacterales;
OC   Enterobacteriaceae; Escherichia.
OX   NCBI_TaxID=562;
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RA   Lakshmi V.V., Thomas C.M.;
RT   "Curing of the F-like plasmid TP181 by plumbagin is due to interference
RT   with both replication and maintenance functions.";
RL   Submitted (APR-1996) to the EMBL/GenBank/DDBJ databases.
CC   -!- FUNCTION: Toxic component of a type II toxin-antitoxin (TA) system,
CC       functioning in plasmid maintainence. Responsible for the post-
CC       segregational killing (PSK) of plasmid-free cells, also referred to as
CC       a plasmid addiction system. Half-life of over 2 hours. Interferes with
CC       the activity of DNA gyrase, inducing it to form a covalent GyrA-DNA
CC       complex that cannot be resolved, thus promoting breakage of plasmid and
CC       chromosomal DNA. Toxicity is inhibited by labile antitoxin CcdA, which
CC       blocks the activity of CcdB; CcdA also removes bound CcdB protein from
CC       the CcdB-GyrA complex by forming a CcdA-CcdB complex, a process termed
CC       rejuvenation. Functions as a transcriptional corepressor for the ccdAB
CC       operon, repression also requires CcdA (By similarity). {ECO:0000250}.
CC   -!- SUBUNIT: Homodimer. Forms a complex with GyrA, probably a tetramer
CC       GyrA(2)CcdB(2), in which GyrA is inactive. Forms a complex with toxin
CC       CcdB; the CcdA-CcdB(2) trimer is sufficient for rejuvenation, whereas
CC       maximal operon repression occurs with CcdA(2)CcdB(2) (By similarity).
CC       {ECO:0000250}.
CC   -!- SIMILARITY: Belongs to the CcdB toxin family. {ECO:0000305}.
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DR   EMBL; U51588; AAA96062.1; -; Genomic_DNA.
DR   AlphaFoldDB; Q46996; -.
DR   SMR; Q46996; -.
DR   GO; GO:0008657; F:DNA topoisomerase type II (double strand cut, ATP-hydrolyzing) inhibitor activity; IEA:InterPro.
DR   GO; GO:0006276; P:plasmid maintenance; IEA:InterPro.
DR   Gene3D; 2.30.30.110; -; 1.
DR   InterPro; IPR002712; CcdB.
DR   InterPro; IPR011067; Plasmid_toxin/cell-grow_inhib.
DR   Pfam; PF01845; CcdB; 1.
PE   3: Inferred from homology;
KW   Plasmid; Repressor; Toxin-antitoxin system; Transcription;
KW   Transcription regulation.
FT   CHAIN           1..101
FT                   /note="Toxin CcdB"
FT                   /id="PRO_0000068388"
SQ   SEQUENCE   101 AA;  11748 MW;  488A05CEC68E94FE CRC64;
     MQFKVYTYKR ESRYRLFVDV QSDIIDTPGR RMVIPLASAR LLSDKVSREL YPVVHIGDES
     WRMMTTQMVS VPVSVIGEEV ADLSHRENDI KNAINLMFWG I