Colicin: Difference between revisions
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<Structure load='1cii' size='300' side='right' caption='Crystal structure of Colicin Ia, the first colicin to be identified. (PDB entry [[1cii]])' | Scene= Colicin/3domains/1 /> | |||
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 <ref> PMID: 16166536 </ref>. Bacteriocins are named after their species of origin; colicins are so-called because they are produced by <i>E. Coli</i><ref>PMID: 17347522 </ref>. Because of their narrow killing spectrum which focuses primarily on the species which has made the peptide (or occasionally closely related species<ref> PMID: 12423779 </ref>), bacteriocins are important in microbial biodiversity and the stable co-existence of the bacterial populations<ref> PMID: 11792831 </ref><ref>PMID: 12110887 </ref>. | 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 <ref> PMID: 16166536 </ref>. Bacteriocins are named after their species of origin; colicins are so-called because they are produced by <i>E. Coli</i><ref>PMID: 17347522 </ref>. Because of their narrow killing spectrum which focuses primarily on the species which has made the peptide (or occasionally closely related species<ref> PMID: 12423779 </ref>), bacteriocins are important in microbial biodiversity and the stable co-existence of the bacterial populations<ref> PMID: 11792831 </ref><ref>PMID: 12110887 </ref>. | ||
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<ref> PMID: 7577966 </ref>. | 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<ref> PMID: 7577966 </ref>. | ||
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Table taken from <ref>PMID: 21060316 </ref> except where indicated. | Table taken from <ref>PMID: 21060316 </ref> except where indicated. | ||
==Directed evolution and Colicin7/Immunity-proteins complexes== | ==Directed evolution and Colicin7/Immunity-proteins complexes<ref>PMID:19749752</ref>== | ||
<StructureSection load='3gkl' size='500' frame='true' align='right' scene='3gkl/Al/1' > | <StructureSection load='3gkl' size='500' frame='true' align='right' scene='3gkl/Al/1' > | ||
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 <scene name='3gkl/Al/3'>variants</scene> <font color='lime'><b>R12-2</b></font> ([[3gkl]]; T20A, N24D, T27A, S28T, V34D, V37J, E41G, and K57E) and <font color='darkred'><b>R12-13</b></font> ([[3gjn]]; N24D, D25E, T27A, S28T, V34D, V37J, and Y55W) in complex with ColE7 were solved. | 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 <scene name='3gkl/Al/3'>variants</scene> <font color='lime'><b>R12-2</b></font> ([[3gkl]]; T20A, N24D, T27A, S28T, V34D, V37J, E41G, and K57E) and <font color='darkred'><b>R12-13</b></font> ([[3gjn]]; N24D, D25E, T27A, S28T, V34D, V37J, and Y55W) in complex with ColE7 were solved. | ||