A leukocidin is a type of cytotoxin created by some types of bacteria ( Staphylococcus). 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 , 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 ("-cide") leukocytes. Leukocidins target ,
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.
Subunits: S and F
The F subunit stands for the "fast" subunit while the S subunit stands for the "slow" subunit.
The S subunit is the first to bind the lipid bilayer, recognizing the cell surface receptor. Once bound, the F subunit dimerizes with the S subunit to initiate pore assembly.
Variatiants
There are exceptions to the typical binding pattern of leukocidins. For example:
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LukPQ: In this case, the F subunit (rather than the S subunit) recognizes the cell surface receptor.
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LukAB: This leukocidin binds to the integrin CD11b, not a G-protein coupled receptor.
Examples
One notable type of leukocidin is the Panton-Valentine leukocidin.
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