Colicin A: Difference between revisions
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Colicin A is a type of [[Colicin]], a bacteriocin made by <i>E. | '''Colicin A''' is a type of [[Colicin]], a bacteriocin made by <i>E. coli</i> which acts against other nearby <i>E. coli</i> to kill them by forming a pore in the membrane, leading to depolarisation of the membrane which kills the cell. | ||
==Synthesis | ==Synthesis== | ||
Colicin A is synthesised through a single operon, also containing the colicin A lysis protein encoding gene, <i>Cal</i>, and the ColA [[Colicin Immunity Protein]], [[Colicin_Immunity_Protein]]. The <i>Cal</i> gene is also involved in the expression of the colicin A operon - without the <i>cal</i> gene the amount of colicin A produced decreases<ref> PMID: 9245818 </ref>. The <i>cal</i> gene product is likely to be an activator of colicin A expression, including its own expression. The N terminal region of the <i>cal</i> gene product is particularly involved in the regulation of col A synthesis. A separate, unidentified, product (which may be a heat-shock protein) could also be involved, and complement the <i>cal</i> gene product<ref> PMID: 9245818 </ref>. | |||
The expression of the col A operon provokes a shut-off of chromosomal protein expression, which is due to the expression of the lysis gene. This shut-off gives the col A production a priority over other cellular proteins in their synthesis. | |||
Synthesis of col A starts immediately after induction. At lower temperatures, like 30<sup>o</sup>c, there is a lag phase to this synthesis, which does not end in null ''cal'' mutants. At 37-42<sup>o</sup>c the lag is very short, and a large amount of col A is produced very rapidly. The signal to speed up synthesis from the lag phase involves the ''cal'' gene product, alongside the other unidentified gene product at normal and high temperatures<ref> PMID: 9245818</ref>. | |||
== | ''Cal'' has a self-regulatory role in the expression of both itself and the col A gene, which may be common to all colicin lysis proteins. | ||
==Release== | |||
Extracellular release of col A is non-specific<ref> PMID: 3311727 </ref>. No mutations in the central or N terminal regions of col A were found to have any effect on the release, or on the efficiency of the release. When the three domains of col A were separated they also still continued to be released at normal levels. A mutation was also inserted in the C terminus to promote aggregation of the protein in the cytoplasm, and this also had no effect on the secretion of col A, so there is no interaction between N and C termini in the release of Col A<ref> PMID: 3311727</ref>. | |||
The process of release is therefore non-specific with respect to the colicin itself, and is dependent only on the expression of the ''cal'' gene. This causes release of col A through the non-specific permeabilisation of the cell envelope<ref> PMID: 3311727 </ref>. | |||
==Uptake== | |||
{{STRUCTURE_3iax | PDB=3iax | SCENE= Colicin_A/Tolbcola/1 }} | |||
Colicin A binds to the BtuB Vitamin B12 outer membrane receptor of the target cell, and uses the [[Tol]] system to translocate across the membrane, specifically TolQRAB, alongside the OmpF protein. Its use of the Tol system means that Colicin A is in the A group of colicins. | |||
This structure shows the <scene name='Colicin_A/Tolbbox/1'>TolB box</scene> of colA bound to <scene name='Colicin_A/Tolb/1'>TolB</scene>. | |||
==Cytotoxic activity== | |||
Colicin A exhibits [[Pore Formation]] activity, which means that its cytotoxic domain inserts into the membrane of the target cell, resulting in the depolarisation of the cell membrane. <i>E. coli</i> uses the polarisation of its cell membrane to generate energy, so with this not functioning a number of energy-requiring cellular functions are inhibited<ref> PMID:4905544 </ref>, and the cell ultimately dies, after an arrest of motility within 3 minutes<ref> PMID: 4905544 </ref>. ColA denatured first in urea kills the cell more quickly than natively folded ColA<ref> PMID: 1537329 </ref>. | |||
Col A when present in an <i>E. coli</i> cell is able to affect macromolecular synthesis throughout the cell, affecting many of the processes in the cell. One such affected system is nucleic acid synthesis; it is halted very soon after Col A is added to the system<ref>PMID:4905544 </ref>. | Col A when present in an <i>E. coli</i> cell is able to affect macromolecular synthesis throughout the cell, affecting many of the processes in the cell. One such affected system is nucleic acid synthesis; it is halted very soon after Col A is added to the system<ref>PMID:4905544 </ref>. | ||
Colicin A also has a negative impact on the availability of ATP-dependent active transports, such as some permease activities, such as the uptake of labelled isoleucine<ref> PMID:4905544 </ref>. | |||
==3D structures of colicin A== | |||
[[Colicin]] | |||
The structure determination of the C-terminal domain of protein was done by Dr. Parker and colleagues<ref> PMID:2909895 </ref><ref> PMID:1373773 </ref>. It enabled to better understand the stability of hydrophobic pockets, the energy transfer among the three tryptophan residue in that domain, and the creation of double-cysteine mutants to understand the transition from soluble to membrane associated protein<ref> PMID:8663026 </ref><ref> PMID:7849033 </ref><ref> PMID:7716161 </ref>. | |||
==References== | ==References== | ||
<references/> | <references/> | ||