Bacterial protein toxins and lipids: pore formation or toxin entry into cells.

Lipids are hydrophobic molecules which play critical functions in cells, in particular, they are essential constituents of membranes, whereas bacterial toxins are mainly hydrophilic proteins. All bacterial toxins interact first with their target cells by recognizing a surface receptor, which is either a lipid or a lipid derivative, or another compound but in a lipid environment. Most bacterial toxins are PFTs (pore-forming toxins) which oligomerize and insert into the lipid bilayer. A common mechanism of action involves the formation of a beta-barrel structure, resulting from the assembly of individual beta-hairpin(s) from individual monomers. An essential step for intracellular active toxins is to translocate their enzymatic part into the cytosol. Some toxins use a translocation mechanism based on pore formation similar to that of PFTs, others undergo a yet unclear 'chaperone' process.