Colicin A

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Colicin A is a type of Colicin, a bacteriocin made by E. Coli which acts against other nearby E. Coli to kill them by forming a pore in the membrane, leading to depolarisation of the membrane which kills the cell.

Contents

Synthesis and release

Colicin A is synthesised through a single operon, containing the colicin A lysis protein encoding gene, Cal. The Cal gene is also involved in the expression of the colicin A operon - without the cal gene the amount of colicin A produced decreases[1]. The cal gene product is likely to be an activator of colicin A expression, including its own expression. A separate, unidentified, product (which may be a heat-shock protein) could also be involved, and complement the cal gene product[2]. 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.

Mechanism of uptake

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.

Killing Activities

Colicin A is a pore-forming colicin, which means that its cytotoxic domain inserts into the membrane of the target cell, resulting in the depolarisation of the cell membrane. E. coli uses the polarisation of its cell membrane to generate energy, so with this not functioning a number of energy-requiring cellular functions are inhibited[3], and the cell ultimately dies, after an arrest of motility within 3 minutes[4].

Col A when present in an E. coli 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[5]. 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[6].


References

  1. ↑ Cavard D. Role of the colicin A lysis protein in the expression of the colicin A operon. Microbiology. 1997 Jul;143 ( Pt 7):2295-303. PMID:9245818
  2. ↑ Cavard D. Role of the colicin A lysis protein in the expression of the colicin A operon. Microbiology. 1997 Jul;143 ( Pt 7):2295-303. PMID:9245818
  3. ↑ Nagel de Zwaig R. Mode of action of colicin A. J Bacteriol. 1969 Sep;99(3):913-4. PMID:4905544
  4. ↑ Nagel de Zwaig R. Mode of action of colicin A. J Bacteriol. 1969 Sep;99(3):913-4. PMID:4905544
  5. ↑ Nagel de Zwaig R. Mode of action of colicin A. J Bacteriol. 1969 Sep;99(3):913-4. PMID:4905544
  6. ↑ Nagel de Zwaig R. Mode of action of colicin A. J Bacteriol. 1969 Sep;99(3):913-4. PMID:4905544

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