# Colicin > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Colicin > Markdown URL: https://mediated.wiki/source/Colicin.md > Source: https://en.wikipedia.org/wiki/Colicin > Source revision: 1325910671 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Type of bacteriocin produced by and toxic to some strains of Escherichia coli}} {{Distinguish|Colchicine|Colistin}}{{Infobox protein family | Symbol = Colicin | Name = Colicin | image = PDB 2ivz EBI.jpg | width = | caption = Structure of [TolB](/source/TolB) in complex with a peptide of the colicin e9 t-domain | Pfam = PF03515 | Pfam_clan = CL0446 | InterPro = IPR003058 | SMART = | PROSITE = | MEROPS = | SCOP = 1jch | TCDB = | OPM family = | OPM protein = | CAZy = | CDD = }} A '''colicin''' is a type of [bacteriocin](/source/bacteriocin) produced by and toxic to some strains of ''[Escherichia coli](/source/Escherichia_coli)''.{{cite journal |vauthors=Feldgarden M, Riley MA |year=1999 |title=The phenotypic and fitness effects of colicin resistance in Escherichia coli K-12 |journal=Evolution |volume=53 |issue=4 |pages=1019–27 |doi=10.2307/2640807 |jstor=2640807 |pmid=28565527}} Colicins are released into the environment to reduce competition from other [bacterial strain](/source/bacterial_strain)s. Colicins bind to [outer membrane receptor](/source/TonB-dependent_receptors)s, using them to [translocate](/source/Translocase_of_the_outer_membrane) to the cytoplasm or cytoplasmic membrane, where they exert their cytotoxic effect, including depolarisation of the cytoplasmic membrane, [DNase](/source/DNase) activity, [RNase](/source/RNase) activity, or inhibition of [murein](/source/murein) synthesis. ==Structure== Channel-forming colicins (colicins A, B, E1, Ia, Ib, and N) are [transmembrane protein](/source/transmembrane_protein)s that depolarize the cytoplasmic membrane, leading to dissipation of cellular energy.{{cite journal |vauthors=Kang C, Postle K, Chen G, Park H, Youn B, Hilsenbeck JL |title=Crystal structure of the cytotoxic bacterial protein colicin B at 2.5 A resolution |journal=Mol. Microbiol. |volume=51 |issue=3 |pages= 711–20|year=2004 |pmid=14731273 |doi=10.1111/j.1365-2958.2003.03884.x|doi-access=free }} These colicins contain at least three domains: an N-terminal translocation domain responsible for movement across the [outer membrane](/source/Bacterial_outer_membrane) and [periplasmic space](/source/periplasmic_space) (T domain); a central domain responsible for receptor recognition (R domain); and a C-terminal [cytotoxic](/source/cytotoxic) domain responsible for channel formation in the cytoplasmic membrane (C domain).{{cite journal |vauthors=Cramer WA, Zakharov SD, Antonenko YN, Kotova EA |year=2004 |title=On the role of lipid in colicin pore formation |journal=Biochim. Biophys. Acta |volume=1666 |issue=1 |pages=239–49 |doi=10.1016/j.bbamem.2004.07.001 |pmid=15519318 |doi-access=free}}Cascales et al. (2007). ''Colicin Biology''. Microbio. and Mol. Bio. Rev. 71(1), 158-229. [http://mmbr.asm.org/cgi/content/abstract/71/1/158 Abstract] [http://mmbr.asm.org/cgi/reprint/71/1/158 pdf]{{Cite journal |last1=Wiener |first1=Michael |last2=Freymann |first2=Douglas |last3=Ghosh |first3=Partho |last4=Stroud |first4=Robert M. |date=January 1997 |title=Crystal structure of colicin Ia |url=https://www.nature.com/articles/385461a0 |journal=Nature |language=en |volume=385 |issue=6615 |pages=461–464 |doi=10.1038/385461a0 |pmid=9009197 |bibcode=1997Natur.385..461W |s2cid=4237547 |issn=1476-4687|url-access=subscription }} R domain regulates the target and binds to the receptor on the sensitive cell. T domain is involved in translocation, co-opting the machinery of the target cell. The C domain is the 'killing' domain and may produce a pore in the target [cell membrane](/source/cell_membrane), or act as a [nuclease](/source/nuclease) to chop up the [DNA](/source/DNA) or [RNA](/source/RNA) of the target cell. ==Translocation== Most colicins are able to translocate the outer membrane by a two-receptor system, where one receptor is used for the initial binding and the second for translocation. The initial binding is to [cell surface receptors](/source/TonB-dependent_receptors) such as the outer membrane proteins OmpF, FepA, BtuB, Cir and FhuA; colicins have been classified according to which receptors they bind to. The presence of specific periplasmic proteins, such as [TolA, TolB, TolC](/source/Outer_membrane_efflux_proteins), or TonB, are required for translocation across the membrane.{{cite journal |vauthors=Cao Z, Klebba PE |title=Mechanisms of colicin binding and transport through outer membrane porins |journal=Biochimie |volume=84 |issue=5–6 |pages=399–412 |year=2002 |pmid=12423783 |doi=10.1016/S0300-9084(02)01455-4}} [Cloacin](/source/Cloacin_immunity_protein){{cite journal |vauthors=van den Elzen PJ, Gaastra W, Spelt CE, de Graaf FK, Veltkamp E, Nijkamp HJ | title = Molecular structure of the immunity gene and immunity protein of the bacteriocinogenic plasmid Clo DF13 | journal = Nucleic Acids Res. | volume = 8 | issue = 19 | pages = 4349–63 |date=October 1980 | pmid = 6253914 | pmc = 324244 | doi = 10.1093/nar/8.19.4349}} DF13 is a bacteriocin that inactivates ribosomes by hydrolysing 16S RNA in 30S ribosomes at a specific site.{{cite journal |vauthors=van den Elzen PJ, Veltkamp E, Nijkamp HJ, Walters HH |title=Molecular structure and function of the bacteriocin gene and bacteriocin protein of plasmid Clo DF13 |journal=Nucleic Acids Res. |volume=11 |issue=8 |pages=2465–2477 |year=1983 |pmid=6344017 |doi=10.1093/nar/11.8.2465 |pmc=325896}} ==Resistance== Because they target specific receptors and use specific translocation machinery, cells can make themselves resistant to the colicin by repressing or deleting the genes for these proteins. Such resistant cells may suffer the lack of a key nutrient (such as [iron](/source/iron) or a [B vitamin](/source/vitamin_B)), but benefit by not being killed. Colicins exhibit a '1-hit killing kinetic' {{Citation needed|date=December 2018}} which does not necessarily mean a single molecule is sufficient to kill, but certainly that it only takes a small number. In his 1969 Nobel Laureate speech, [Salvador E. Luria](/source/Salvador_E._Luria) speculated that colicins could only be this toxic by causing a [domino effect](/source/domino_effect) that destabilized the cell membrane.[http://nobelprize.org/nobel_prizes/medicine/laureates/1969/luria-lecture.html Luria, S. E. (1969) Nobel Lecture] He was not entirely correct, but pore-forming colicins do depolarize the membrane and thus eliminate the energy source for the cell. The colicins are highly effective [toxin](/source/toxin)s.{{cn|date=December 2022}} ==Genetic organisation== Virtually all colicins are carried on [plasmid](/source/plasmid)s. The two general classes of [colicinogenic plasmids](/source/Bacteriocinogen) are large, low-copy-number plasmids, and small, high-copy-number plasmids. The larger plasmids carry other genes, as well as the colicin operon. The colicin operons are generally organized with several major [gene](/source/gene)s. These include a colicin structural gene, an immunity gene, and a [bacteriocin release protein](/source/bacteriocin_release_protein) (BRP), or [lysis](/source/lysis), gene. The immunity gene is often produced constitutively, while the BRP is generally produced only as a read-through of the [stop codon](/source/stop_codon) on the colicin structural gene. The colicin itself is repressed by the [SOS response](/source/SOS_response) and may be regulated in other ways as well.{{Cite journal |last1=Mader |first1=Andreas |last2=von Bronk |first2=Benedikt |last3=Ewald |first3=Benedikt |last4=Kesel |first4=Sara |last5=Schnetz |first5=Karin |last6=Frey |first6=Erwin |last7=Opitz |first7=Madeleine |date=2015-03-09 |title=Amount of Colicin Release in Escherichia coli Is Regulated by Lysis Gene Expression of the Colicin E2 Operon |journal=PLOS ONE |volume=10 |issue=3 |article-number=e0119124 |doi=10.1371/journal.pone.0119124 |issn=1932-6203 |pmc=4353708 |pmid=25751274 |bibcode=2015PLoSO..1019124M |doi-access=free }} Retaining the colicin plasmid is very important for cells that live with their relatives, because if a cell loses the immunity gene, it quickly becomes subject to destruction by circulating colicin. At the same time, colicin is only released from a producing cell by the use of the lysis protein, which results in that cell's death. This suicidal production mechanism would appear to be very costly, except for the fact that it is regulated by the [SOS response](/source/SOS_response), which responds to significant [DNA](/source/DNA) damage. In short, colicin production may only occur in terminally ill cells. The Professor Kleanthous Research Group at the [University of Oxford](/source/University_of_Oxford) study colicins extensively as a model system for characterising and investigating protein-protein interactions and recognition.{{cite web|title=Kleanthous Research Group|url=http://www.bioch.ox.ac.uk/aspsite/index.asp?pageid=910|access-date=23 May 2017|archive-date=6 May 2017|archive-url=https://web.archive.org/web/20170506122448/https://www.bioch.ox.ac.uk/aspsite/index.asp?pageid=910}} BACTIBASE{{cite journal |title=BACTIBASE: a new web-accessible database for bacteriocin characterization |vauthors=Hammami R, Zouhir A, Ben Hamida J, Fliss I |journal=BMC Microbiology |year=2007 |volume=7 |page=89 |pmid=17941971 |doi=10.1186/1471-2180-7-89 |pmc=2211298 |doi-access=free }}{{cite journal |title=BACTIBASE second release: a database and tool platform for bacteriocin characterization. |vauthors=Hammami R, Zouhir A, Le Lay C, Ben Hamida J, Fliss I |journal=BMC Microbiology |year=2010 |volume=10 |page=22 |pmid=20105292 |doi=10.1186/1471-2180-10-22 |pmc=2824694 |doi-access=free }} database is an open-access database for bacteriocins including colicins ([http://bactibase.hammamilab.org/bacteriocinslist.php?Name=colicin view complete list]). == References == {{reflist|2}} ==External links== * [https://web.archive.org/web/20070401085510/http://mbe.oxfordjournals.org/cgi/content/abstract/10/6/1380 Molecular mechanisms of colicin evolution] [https://web.archive.org/web/20060224032938/http://mbe.oxfordjournals.org/cgi/reprint/10/6/1380 pdf] * [http://mic.sgmjournals.org/cgi/content/full/146/7/1671 The newly characterized colicin Y provides evidence of positive selection in pore-former colicin diversification] * [http://opm.phar.umich.edu/families.php?superfamily=93 Colicin OPM database] * [http://www.proteopedia.org/wiki/index.php/Colicin 3D interactive pages about colicins] * [http://www.tcdb.org/tcdb/index.php?tc=1.C.1 Transport Classification Database listing for colicin] * [http://www.ebi.ac.uk/pdbe-srv/view/search?search_type=advanced&text=colicin Protein Data Bank colicin listing] {{InterPro content|IPR000290}} Category:Bacteriocins Category:Membrane channels Category:Peripheral membrane proteins Category:Escherichia coli Category:Bacterial toxins Category:Bactericides Category:Antimicrobial peptides --- Adapted from the Wikipedia article [Colicin](https://en.wikipedia.org/wiki/Colicin) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Colicin?action=history)). 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