Leukocidin
A leukocidin is a type of cytotoxin created by some types of bacteria. It is a type of pore-forming toxin. Leukocidins fall into the category of bacterial invasin. Invasins are enzymatic secretions that help bacteria invade the host tissue to which they are attached. Although similar to exotoxins, invasins are different in two respects: they work through much less specific mechanisms than exotoxins, and their actions are generally more localized.
Leukocidins get their names by killing leukocytes. Leukocidins target phagocytes, natural killer cells, dendritic cells, and T lymphocytes, and therefore affect both innate and adaptive immune responses.
Mechanism of action
Leukocidins are pore-forming toxins, and their model for pore formation is step-wise.First, the cytotoxin's "S" subunit recognizes specific protein-containing receptors, typically G-protein coupled receptors, or an integrin on the host cell's surface. The S subunit then recruits a second, "F" subunit. The two subunits dimerize on the host cell surface. This dimerization is followed by oligomerization involving three additional leukocidin dimers, resulting in an octameric prepore complex.
The prepore undergoes a structural transition in which its prestem domain extends into the lipid bilayer, forming a beta barrel that pierces the target cell membrane, thereby disrupting the structure of the cell and leading to lysis.