Colicin

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Template:STRUCTURE 1cii

Colicins are a type of bacteriocin - peptide and protein antibiotics released by bacteria to kill other bacteria of the same species, in order to provide a competitive advantage for nutrient acquisition [1]. Bacteriocins are named after their species of origin; colicins are so-called because they are produced by E. Coli[2]. Because of their narrow killing spectrum which focuses primarily on the species which has made the peptide (or occasionally closely related species[3]), bacteriocins are important in microbial biodiversity and the stable co-existence of the bacterial populations[4][5].

Colicin peptides are plasmid-encoded. The peptide is released by the cell into the area surrounding it, and then parasitises proteins present in the host cell membrane to translocate across into the host cell. Many protein-protein interactions are involved in the cell entry, and the main system is involved in the grouping of colicins into two families: Group A colicins use the Tol system to enter the host cell, and Group B use the Ton system. Once inside the host cell, the cell killing follows 1st order kinetics - ie one molecule is theoretically sufficient to kill the cell[6].

The structure of all colicins, of which over 20 have been identified, follows a 3 domain design:
At the N terminus is the Translocation domain (T-): Residues in ColIa.
The Receptor binding domain is at the centre of the peptide (R-): Residues in ColIa.
The C terminus contains the Cytotoxic domain (C-): Residues in ColIa[7].

The 3 domain structure of all colicins

For more details see Pore Formation.

Synthesis, Production and ReleaseSynthesis, Production and Release

Synthesis of many colicins is repressed by the LexA protein, which is part of the SOS regulon[8].

The structure of a typical colicin operon, highlighting the 3 proteins encoded together.

Targeting and ReceptorsTargeting and Receptors

Colicins vary significantly in the receptors that they target to initiate their uptake. The majority of the group A colicins use the BtuB receptor, which is present on E. coli as a vitamin B12 uptake receptor. Once bound to the receptor, the coiled-coil receptor binding domain unfolds, in an essential step that removes the immunity protein and triggers translocation[9]. Other colicins use other receptors - generally involved in the uptake of small metabolite growth factors.

Colicin UptakeColicin Uptake

Colicins are divided into two groups depending on the method of uptake which they target. Group A colicins use the Tol system to bind to and enter the target cell, and group B use the Ton system. The Tol system consists of 5 proteins - TolA, TolB, TolR, TolQ and Pal[10], and group A proteins using this often recruit a second co-receptor involved in translocation, usually OmpF or TolC, but could be OmpC and PhoE[11]. The Ton system consists of TonB, ExbB and ExbD[12], and no known co-receptor is utilised in translocation[13].It could be possible that Ton-dependent colicins are indiscriminate in use of coreceptors, or that the colicins move down the outside wall of a β barrel protein[14]. It is known that colicins do unfold during translocation, but the peptides resulting from this exceed the diameter of pores formed by any of the molecules mentioned above[15][16]. However, while unfolding does occur, this is not induced by receptor binding in either Tol or Ton dependent colicins[17].

Understanding how the colicins can cross the membrane is highly important, as if this could be targeted and exploited it could be useful for novel therapeutic agents[18]. It is also estimated that a single colicin molecule is sufficient to kill the bacterial cell, following first order kinetics[19].

Killing ActivitiesKilling Activities

Colicins kill their target cell through a variety of different methods. The main killing activities are carried out through Pore Formation, DNase Activity and 16s rRNase activity, and some colicins also exhibit tRNase activity.

The killing activities carried out by colicins could be used medicinally as an alternative to antibiotics in the case where the specific strain of E. coli can be identified[20], and as potential natural replacements for food preservatives[21].


List of colicins, with their translocation proteins and cytotoxic activity
Colicin Group OM Receptor Translocation Proteins Cytotoxic activity Immunity protein
Colicin A A BtuB OmpF/TolQRAB Pore-forming Colicin_Immunity_Protein[22]
Colicin E1 A BtuB TolC/TolAQ Pore-forming ImmE1[23]
Colicin E2 A BtuB OmpF/TolQRAB DNase Im2[24]
Colicin E3 A BtuB OmpF/TolQRAB 16s rRNase Im3[25]
Colicin E4 A BtuB OmpF/TolQRAB 16s rRNase Im4[26]
Colicin E5 A BtuB OmpF/TolQRAB tRNase ImmE5[27]
Colicin E6 A BtuB OmpF/TolQRAB 16s rRNase ImmE6[28]
Colicin E7 A BtuB OmpF/TolQRAB DNase Im7[29]
Colicin E8 A BtuB OmpF/TolQRAB DNase Im8[30]
Colicin E9 A BtuB OmpF/TolQRAB DNase Im9[31]
Colicin N A OmpF OmpF/TolQRA Pore-forming Cni[32]
Colicin S4 A OmpW OmpF/TolQRAB Pore-forming Csi[33]
Colicin K A Tsx OmpF/TolQRAB Pore-forming ?
Cloacin DF13 A lutA [34] TolQRA [35] 16s rRNase [36]
Colicin U A ? OmpAF, TolQRAB Pore-forming Cui[37]
Colicin 5 B Tsx TolC/TonB, ExbBD Pore-forming Cfi[38]
Colicin 6 B Tsx TolC/TonB, ExbBD Pore-forming ?
Colicin 7 B Tsx TolC/TonB, ExbBD Pore-forming ?
Colicin 8 B Tsx TolC/TonB, ExbBD Pore-forming ?
Colicin 9 B Tsx TolC/TonB, ExbBD Pore-forming ?
Colicin 10 B Tsx TolC/TonB, ExbBD Pore-forming Cti[39]
Colicin Ia B Cir Cir/TonB, ExbBD Pore-forming Iia[40]
Colicin Ib B Cir Cir/TonB, ExbBD Pore-forming Imm
Colicin B B FepA ?/TonB, ExbBD Pore-forming Cbi[41]
Colicin D B FepA ?/TonB, ExbBD tRNase ImmD[42]
Colicin M B FhuA ?/TonB, ExbBD Inhibition of PG synthesis Cmi[43]
Colicin V B Cir? [44] TonB, ExbB Disruption of membrane potential Cvi[45]
Colicin Js B CjrBC [46] ExbBD, VirB [47] ? Cji [48]
Colicin Y ? ? ? Pore-forming [49] Cyi[50]

Table taken from [51] except where indicated.

Directed evolution and Colicin7/Immunity-proteins complexes[52]Directed evolution and Colicin7/Immunity-proteins complexes[52]

Iterative rounds of random mutagenesis and selection of immunity protein 9 (colored yellow) toward higher affinity for ColE7, and selectivity (against ColE9 inhibition), led to significant increase in affinity and selectivity. Several evolved variants were obtained. The crystal structures of the two final generation R12-2 (3gkl; T20A, N24D, T27A, S28T, V34D, V37J, E41G, and K57E) and R12-13 (3gjn; N24D, D25E, T27A, S28T, V34D, V37J, and Y55W) in complex with ColE7 were solved.

of the immunity protein 9 (Im9, 1bxi, colored yellow), evolved variant R12-2 (lime), and immunity protein 7 (Im7, 7cei, colored blue) reveals their structural identity. However, when the immunity proteins-bound , they demonstrate somewhat different picture. The Im9 and Im7 are differ more in their binding configurations (19°, with Tyr54-Tyr55 as the pivot), while the variant R12-2 is in an intermediate configuration between Im9 and Im7. Of note, in the variant R12-2 (3gkl) and Im9 (1bxi) there are Tyr54 and Tyr55, while in the Im7 (7cei) Tyr55 and Tyr56 are homologous to them. The most are in the loop between helices α1 and α2 in Im9 (yellow, labeled in black) and evolved variant R12-2 (lime, labeled in black). This loop consists of three mutations: N24D, T27A, and S28T in variant R12-2. We can see the deviations in the relative position of helices α1 and α2, in the loop's backbone and in the side chains of residues 24, 26 and 28.

Comparison of the different Im-colicin complexes reveals changes in the binding configuration of the evolved variants which increase affinity toward ColE7 by re-aligning pre-existing Im9 residues. Glu30 of Im9 (1bxi, colored yellow) forms with Arg54 of ColE9 (orange), whereas Asp51 have not direct side chain–side chain interactions. Asp31 of Im7 (blue) (corresponding to Im9 Glu30) is involved in to Arg520 and Lys525 of ColE7 (darkmagenta), while Asp52 of Im7 (corresponding to Im9 Asp51) is within hydrogen bond distance to Thr531 and Arg530 of ColE7. Glu30 in the variant R12-2 (lime) is shifted and forms a to Arg520 of ColE7 (magenta). Asp51 is within hydrogen bond distance to Thr531 of ColE7. However, the side chains of Lys525 and Arg530, which are very important in salt bridge contacts with Glu30 and Asp51, respectively, in the structure of the ColE7–Im7 complex have a different conformation that eliminates these contacts in evolved variant R12-2.

In the Val37 (colored magenta) forms stabilizing hydrogen bond with Leu33. In the , Ile37 (colored darkmagenta) interacts with two additional residues, Tyr54 and Ser50. Moreover, Ile37 also forms additional hydrogen bond with Gly41 and can thereby have enabled the appearance of the selectivity mutation E41G.

In contrast to the evolved variant R12-2 (3gkl), the evolved variant R12-13 (3gjn) carries the in the conserved region. Both Tyr55 in R12-2 and Trp55 in R12-13 could sustain the

hydrophobic core and create a to Lys528 backbone (3gkl colicin residues are colored in magenta, 3gjn colicin residues are colored blueviolet). However, the additional bulkiness of the Trp contributes in expanding its to Phe541 and Phe513 also leading to the small shift in the alkyl chain of Arg530.

The of the two evolved variants R12-2 (3gkl) and R12-13 (3gjn) is very similar. The variant R12-2 carries . In the bound wildtype Im9 (yellow) Glu41 makes a with the ColE9’s Lys97 (1bxi). While in the R12-13/ColE7 complex the closest ColE7 residues R12-13 Glu41 are Thr531 (3.37Å) and Lys528 (8.85Å) (3gjn). In the R12-2/ColE7 complex the ColE7 residue to R12-2 Gly41 is Thr531 (9.48Å) (3gkl).

complex of colicin E7 and a fragment of colicin immunity protein E9 3gkl

Drag the structure with the mouse to rotate


3D structure of Colicin3D structure of Colicin

Update November 2011

Colicin-AColicin-A

3iax – CfColA translocation domain + EcTolB – Citrobacter freundii
1col – EcColA pore-forming domain

Colicin-BColicin-B

1rh1 - EcColB

Colicin-DColicin-D

1tfk, 1tfo, 1v74 - EcColD catalytic domain + EcColD immunity protein

Colicin-E1Colicin-E1

2i88 – EcColE1 channel-forming domain

Colicin-E2Colicin-E2

2ysu – EcColE2 receptor-binding domain + BtuB

Colicin-E3Colicin-E3

2xfz, 2xg1 – EcColE3 cytotoxic domain (mutant) + Tt30S ribosome – Thermus thermophilus
2zld - EcColE3 cytotoxic domain + outer membrane protein F
1jch – EcColE3 + EcColE3 immunity protein
2b5u – EcColE3 (mutant) + EcColE3 immunity protein
1e44 – EcColE3 nuclease domain + EcColE3 immunity protein
1ujw – EcColE3 receptor-binding domain + BtuB

Colicin-E5Colicin-E5

2djh, 3ao9 – EcColE5 C-terminal domain
3vj7 - EcColE5 C-terminal domain (mutant)
2a8k – EcColE5 catalytic domain
2dfx – EcColE5 C-terminal domain + EcColE5 immunity protein
2fhz – EcColE5 residues 74-180 + EcColE5 immunity protein

Colicin-E7Colicin-E7

1unk - EcColE7
2axc - EcColE7 translocation domain
1m08 - EcColE7 nuclease domain
3fbd, 1zns – EcColE7 (mutant) + DNA
1pt3 - EcColE7 nuclease domain + DNA
1mz8, 7cei - EcColE7 nuclease domain + EcColE7 immunity protein
3gjn - EcColE7 nuclease domain + EcColE9 immunity protein (mutant)
3gkl - EcColE7 nuclease domain (mutant) + EcColE9 immunity protein (mutant)
2jaz, 2jb0, 2jbg, 1znv - EcColE7 nuclease domain (mutant) + EcColE7 immunity protein
2erh, 1ujz - EcColE7 (mutant) + EcColE7 immunity protein (mutant)

Colicin-E9Colicin-E9

1fsj - EcColE9 DNase domain
1v13 - EcColE9 DNase domain (mutant)
1v14, 1v15 - EcColE9 DNase domain (mutant) + DNA
2wpt – EcColE9 (mutant) + EcColE2 immunity protein
2k5x, 1emv, 1bxi – EcColE9 DNase domain + EcColE9 immunity protein
2vln, 2vlo, 2vlp, 2vlq - EcColE9 DNase domain (mutant) + EcColE9 immunity protein
2gze, 2gzg, 2gzi, 2gzj, 2gzf, 2gyk, 1fr2 - EcColE9 DNase domain + EcColE9 immunity protein (mutant)
2ivz - EcColE9 T domain + TolB
3o0e - EcColE9 fragment + outer membrane porin 1A

Colicin-IaColicin-Ia

1cii - EcColIa
2hdi – EcColIA R domain + ColI receptor

Colicin-MColicin-M

2xmx, 3da3, 3da4 – EcColM
2xtq, 2xtr – EcColM (mutant)

Colicin-NColicin-N

1a87 – EcColN receptor-binding domain

Colicin-S4Colicin-S4

3few – EcColS4









ReferencesReferences

  1. ↑ Hands SL, Holland LE, Vankemmelbeke M, Fraser L, Macdonald CJ, Moore GR, James R, Penfold CN. Interactions of TolB with the translocation domain of colicin E9 require an extended TolB box. J Bacteriol. 2005 Oct;187(19):6733-41. PMID:16166536 doi:10.1128/JB.187.19.6733-6741.2005
  2. ↑ Cascales E, Buchanan SK, Duche D, Kleanthous C, Lloubes R, Postle K, Riley M, Slatin S, Cavard D. Colicin biology. Microbiol Mol Biol Rev. 2007 Mar;71(1):158-229. PMID:17347522 doi:10.1128/MMBR.00036-06
  3. ↑ Riley MA, Wertz JE. Bacteriocin diversity: ecological and evolutionary perspectives. Biochimie. 2002 May-Jun;84(5-6):357-64. PMID:12423779
  4. ↑ Czaran TL, Hoekstra RF, Pagie L. Chemical warfare between microbes promotes biodiversity. Proc Natl Acad Sci U S A. 2002 Jan 22;99(2):786-90. Epub 2002 Jan 15. PMID:11792831 doi:10.1073/pnas.012399899
  5. ↑ Kerr B, Riley MA, Feldman MW, Bohannan BJ. Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors. Nature. 2002 Jul 11;418(6894):171-4. PMID:12110887 doi:10.1038/nature00823
  6. ↑ Wallis R, Moore GR, James R, Kleanthous C. Protein-protein interactions in colicin E9 DNase-immunity protein complexes. 1. Diffusion-controlled association and femtomolar binding for the cognate complex. Biochemistry. 1995 Oct 24;34(42):13743-50. PMID:7577966
  7. ↑ Ghosh P, Mel SF, Stroud RM. The domain structure of the ion channel-forming protein colicin Ia. Nat Struct Biol. 1994 Sep;1(9):597-604. PMID:7543362
  8. ↑ Pugsley AP. Genetic analysis of ColN plasmid determinants for colicin production, release, and immunity. J Bacteriol. 1984 May;158(2):523-9. PMID:6327609
  9. ↑ Penfold CN, Healy B, Housden NG, Boetzel R, Vankemmelbeke M, Moore GR, Kleanthous C, James R. Flexibility in the receptor-binding domain of the enzymatic colicin E9 is required for toxicity against Escherichia coli cells. J Bacteriol. 2004 Jul;186(14):4520-7. PMID:15231784 doi:10.1128/JB.186.14.4520-4527.2004
  10. ↑ Braun V, Patzer SI, Hantke K. Ton-dependent colicins and microcins: modular design and evolution. Biochimie. 2002 May-Jun;84(5-6):365-80. PMID:12423780
  11. ↑ Mock M, Pugsley AP. The BtuB group col plasmids and homology between the colicins they encode. J Bacteriol. 1982 Jun;150(3):1069-76. PMID:6281233
  12. ↑ Braun V, Patzer SI, Hantke K. Ton-dependent colicins and microcins: modular design and evolution. Biochimie. 2002 May-Jun;84(5-6):365-80. PMID:12423780
  13. ↑ Cascales E, Buchanan SK, Duche D, Kleanthous C, Lloubes R, Postle K, Riley M, Slatin S, Cavard D. Colicin biology. Microbiol Mol Biol Rev. 2007 Mar;71(1):158-229. PMID:17347522 doi:10.1128/MMBR.00036-06
  14. ↑ Bainbridge G, Armstrong GA, Dover LG, Whelan KF, Lakey JH. Displacement of OmpF loop 3 is not required for the membrane translocation of colicins N and A in vivo. FEBS Lett. 1998 Aug 7;432(3):117-22. PMID:9720908
  15. ↑ Benedetti H, Lloubes R, Lazdunski C, Letellier L. Colicin A unfolds during its translocation in Escherichia coli cells and spans the whole cell envelope when its pore has formed. EMBO J. 1992 Feb;11(2):441-7. PMID:1537329
  16. ↑ Cowan SW, Schirmer T, Rummel G, Steiert M, Ghosh R, Pauptit RA, Jansonius JN, Rosenbusch JP. Crystal structures explain functional properties of two E. coli porins. Nature. 1992 Aug 27;358(6389):727-33. PMID:1380671 doi:http://dx.doi.org/10.1038/358727a0
  17. ↑ Buchanan SK, Lukacik P, Grizot S, Ghirlando R, Ali MM, Barnard TJ, Jakes KS, Kienker PK, Esser L. Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import. EMBO J. 2007 May 16;26(10):2594-604. Epub 2007 Apr 26. PMID:17464289
  18. ↑ Mosbahi K, Walker D, Lea E, Moore GR, James R, Kleanthous C. Destabilization of the colicin E9 Endonuclease domain by interaction with negatively charged phospholipids: implications for colicin translocation into bacteria. J Biol Chem. 2004 May 21;279(21):22145-51. Epub 2004 Mar 23. PMID:15044477 doi:10.1074/jbc.M400402200
  19. ↑ Nomura M. Colicins and related bacteriocins. Annu Rev Microbiol. 1967;21:257-84. PMID:4860260 doi:http://dx.doi.org/10.1146/annurev.mi.21.100167.001353
  20. ↑ Cutler SA, Lonergan SM, Cornick N, Johnson AK, Stahl CH. Dietary inclusion of colicin e1 is effective in preventing postweaning diarrhea caused by F18-positive Escherichia coli in pigs. Antimicrob Agents Chemother. 2007 Nov;51(11):3830-5. Epub 2007 Aug 27. PMID:17724148 doi:10.1128/AAC.00360-07
  21. ↑ Gillor O, Kirkup BC, Riley MA. Colicins and microcins: the next generation antimicrobials. Adv Appl Microbiol. 2004;54:129-46. PMID:15251279 doi:10.1016/S0065-2164(04)54005-4
  22. ↑ Nardi A, Corda Y, Baty D, Duche D. Colicin A immunity protein interacts with the hydrophobic helical hairpin of the colicin A channel domain in the Escherichia coli inner membrane. J Bacteriol. 2001 Nov;183(22):6721-5. PMID:11673448 doi:10.1128/JB.183.22.6721-6725.2001
  23. ↑ Song HY, Cramer WA. Membrane topography of ColE1 gene products: the immunity protein. J Bacteriol. 1991 May;173(9):2935-43. PMID:1708384
  24. ↑ Duche D, Issouf M, Lloubes R. Immunity protein protects colicin E2 from OmpT protease. J Biochem. 2009 Jan;145(1):95-101. Epub 2008 Nov 5. PMID:18990718 doi:10.1093/jb/mvn149
  25. ↑ Jakes K, Zinder ND, Boon T. Purification and properties of colicin E3 immunity protein. J Biol Chem. 1974 Jan 25;249(2):438-44. PMID:4588566
  26. ↑ Carr S, Walker D, James R, Kleanthous C, Hemmings AM. Crystallization of the cytotoxic domain of a ribosome-inactivating colicin in complex with its immunity protein. Acta Crystallogr D Biol Crystallogr. 2000 Dec;56(Pt 12):1630-3. PMID:11092930
  27. ↑ Lau PC, Condie JA. Nucleotide sequences from the colicin E5, E6 and E9 operons: presence of a degenerate transposon-like structure in the ColE9-J plasmid. Mol Gen Genet. 1989 Jun;217(2-3):269-77. PMID:2549375
  28. ↑ Akutsu A, Masaki H, Ohta T. Molecular structure and immunity specificity of colicin E6, an evolutionary intermediate between E-group colicins and cloacin DF13. J Bacteriol. 1989 Dec;171(12):6430-6. PMID:2687234
  29. ↑ Dennis CA, Videler H, Pauptit RA, Wallis R, James R, Moore GR, Kleanthous C. A structural comparison of the colicin immunity proteins Im7 and Im9 gives new insights into the molecular determinants of immunity-protein specificity. Biochem J. 1998 Jul 1;333 ( Pt 1):183-91. PMID:9639578
  30. ↑ Keeble AH, Kleanthous C. The kinetic basis for dual recognition in colicin endonuclease-immunity protein complexes. J Mol Biol. 2005 Sep 23;352(3):656-71. PMID:16109424 doi:10.1016/j.jmb.2005.07.035
  31. ↑ Osborne MJ, Breeze AL, Lian LY, Reilly A, James R, Kleanthous C, Moore GR. Three-dimensional solution structure and 13C nuclear magnetic resonance assignments of the colicin E9 immunity protein Im9. Biochemistry. 1996 Jul 23;35(29):9505-12. PMID:8755730 doi:10.1021/bi960401k
  32. ↑ Geli V, Baty D, Pattus F, Lazdunski C. Topology and function of the integral membrane protein conferring immunity to colicin A. Mol Microbiol. 1989 May;3(5):679-87. PMID:2668695
  33. ↑ Pilsl H, Smajs D, Braun V. Characterization of colicin S4 and its receptor, OmpW, a minor protein of the Escherichia coli outer membrane. J Bacteriol. 1999 Jun;181(11):3578-81. PMID:10348872
  34. ↑ Wooldridge KG, Williams PH. Sensitivity of Escherichia coli to cloacin DF13 involves the major outer membrane protein OmpF. J Bacteriol. 1991 Apr;173(8):2420-4. PMID:2013565
  35. ↑ Thomas JA, Valvano MA. Role of tol genes in cloacin DF13 susceptibility of Escherichia coli K-12 strains expressing the cloacin DF13-aerobactin receptor IutA. J Bacteriol. 1993 Jan;175(2):548-52. PMID:8419302
  36. ↑ Baan RA, Duijfjes JJ, van Leerdam E, van Knippenberg PH, Bosch L. Specific in situ cleavage of 16S ribosomal RNA of Escherichia coli interferes with the function of initiation factor IF-1. Proc Natl Acad Sci U S A. 1976 Mar;73(3):702-6. PMID:768982
  37. ↑ Smajs D, Pilsl H, Braun V. Colicin U, a novel colicin produced by Shigella boydii. J Bacteriol. 1997 Aug;179(15):4919-28. PMID:9244283
  38. ↑ Pilsl H, Braun V. Evidence that the immunity protein inactivates colicin 5 immediately prior to the formation of the transmembrane channel. J Bacteriol. 1995 Dec;177(23):6966-72. PMID:7592492
  39. ↑ Pilsl H, Braun V. Novel colicin 10: assignment of four domains to TonB- and TolC-dependent uptake via the Tsx receptor and to pore formation. Mol Microbiol. 1995 Apr;16(1):57-67. PMID:7651137
  40. ↑ Weaver CA, Redborg AH, Konisky J. Plasmid-determined immunity of Escherichia coli K-12 to colicin Ia Is mediated by a plasmid-encoded membrane protein. J Bacteriol. 1981 Dec;148(3):817-28. PMID:6273383
  41. ↑ Schramm E, Olschlager T, Troger W, Braun V. Sequence, expression and localization of the immunity protein for colicin B. Mol Gen Genet. 1988 Jan;211(1):176-82. PMID:2830463
  42. ↑ Graille M, Mora L, Buckingham RH, van Tilbeurgh H, de Zamaroczy M. Structural inhibition of the colicin D tRNase by the tRNA-mimicking immunity protein. EMBO J. 2004 Apr 7;23(7):1474-82. Epub 2004 Mar 11. PMID:15014439 doi:10.1038/sj.emboj.7600162
  43. ↑ Olschlager T, Schramm E, Braun V. Cloning and expression of the activity and immunity genes of colicins B and M on ColBM plasmids. Mol Gen Genet. 1984;196(3):482-7. PMID:6094976
  44. ↑ Waters VL, Crosa JH. Colicin V virulence plasmids. Microbiol Rev. 1991 Sep;55(3):437-50. PMID:1943995
  45. ↑ Frick KK, Quackenbush RL, Konisky J. Cloning of immunity and structural genes for colicin V. J Bacteriol. 1981 Nov;148(2):498-507. PMID:6271732
  46. ↑ Braun V, Patzer SI, Hantke K. Ton-dependent colicins and microcins: modular design and evolution. Biochimie. 2002 May-Jun;84(5-6):365-80. PMID:12423780
  47. ↑ Smajs D, Weinstock GM. The iron- and temperature-regulated cjrBC genes of Shigella and enteroinvasive Escherichia coli strains code for colicin Js uptake. J Bacteriol. 2001 Jul;183(13):3958-66. PMID:11395459 doi:10.1128/JB.183.13.3958-3966.2001
  48. ↑ Smajs D, Weinstock GM. Genetic organization of plasmid ColJs, encoding colicin Js activity, immunity, and release genes. J Bacteriol. 2001 Jul;183(13):3949-57. PMID:11395458 doi:10.1128/JB.183.13.3949-3957.2001
  49. ↑ Riley MA, Cadavid L, Collett MS, Neely MN, Adams MD, Phillips CM, Neel JV, Friedman D. The newly characterized colicin Y provides evidence of positive selection in pore-former colicin diversification. Microbiology. 2000 Jul;146 ( Pt 7):1671-7. PMID:10878131
  50. ↑ Smajs D, Matejkova P, Weinstock GM. Recognition of pore-forming colicin Y by its cognate immunity protein. FEMS Microbiol Lett. 2006 May;258(1):108-13. PMID:16630264 doi:10.1111/j.1574-6968.2006.00201.x
  51. ↑ Kleanthous C. Swimming against the tide: progress and challenges in our understanding of colicin translocation. Nat Rev Microbiol. 2010 Dec;8(12):843-8. Epub 2010 Nov 9. PMID:21060316 doi:10.1038/nrmicro2454
  52. ↑ Levin KB, Dym O, Albeck S, Magdassi S, Keeble AH, Kleanthous C, Tawfik DS. Following evolutionary paths to protein-protein interactions with high affinity and selectivity. Nat Struct Mol Biol. 2009 Oct;16(10):1049-55. Epub 2009 Sep 13. PMID:19749752 doi:10.1038/nsmb.1670

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