Colicin M

Colicin M is a type of Colicin, a bacteriocin made by E. coli which acts against other nearby E. coli to kill them by inhibiting synthesis of peptidoglycan - murein, preventing synthesis of the cell wall and ultimately leading to cell lysis. of Colicin M.

Synthesis and release

The operon for colicin M is encoded on a plasmid in the cytoplasm of the E. coli. This operon also encodes its Colicin Immunity Protein, Cmi, to protect the membrane of the cell from the activity of the cytotoxic domain, alongside a protein to aid the release of the colicin outside the cell. When produced, the immunity protein binds to and inhibits the enzymatic cytotoxic domain.

Mechanism of uptake

The receptor binding domain of the colicin binds to the outer membrane receptor FhuA on the target cell; it is a constitutively expressed protein parasitised by the colicin. The translocation domain then recruits proteins from the Ton system to translocate the protein across the membrane and into the cytoplasm.

Killing Activities

ColM shows enzymatic properties of degradation of lipid I and lipid II peptidoglycan intermediates. The cleavage occurs between the lipid moiety and the pyrophosphoryl groups. This then leads to the arrest of peptidoglycan polymerisation^[1], rather than the direct degradation of the peptidoglycan^[2].

References

1. ↑ El Ghachi M, Bouhss A, Barreteau H, Touze T, Auger G, Blanot D, Mengin-Lecreulx D. Colicin M exerts its bacteriolytic effect via enzymatic degradation of undecaprenyl phosphate-linked peptidoglycan precursors. J Biol Chem. 2006 Aug 11;281(32):22761-72. Epub 2006 Jun 15. PMID:16777846 doi:10.1074/jbc.M602834200
2. ↑ Schaller K, Dreher R, Braun V. Structural and functional properties of colicin M. J Bacteriol. 1981 Apr;146(1):54-63. PMID:7012126