Actin is a family of globular multifunctional proteins that form microfilaments in the cytoskeleton and filaments in muscle fibrils. It can exist as a free monomer called G-actin (globular) or as part of a linear polymer filament called F-actin (filamentous). Both of these are essential for important cell functions, such as cell movement and shrinkage during movement and cell division. Actin depolymerization was initiated by washing away free actin monomer with the polymerization buffer containing ATP. After washing off the monomer from the newly polymerized ATP-actin filaments, the initial rate of depolymerization is slower. But over time, the rate of decomposition increases to the rate of ADP-actin subunits.
Latrunculin A (also known as LAT-A), a toxin, binds to actin monomers, and inhibits polymerization of actin. And this compound is the most widely used reagent to depolymerize actin filaments in experiments on live cells. Latrunculin A has two effects on the polymerization of Mg-ATP-actin, both of which come from the monomer chelation mechanism. First, Latrunculin A reduces the number of actin filaments, indicating that it slows down spontaneous nucleation that is very sensitive to monomer concentration. Second, Latrunculin A reduces the elongation of the barbed end. In addition, Latrunculin A also inhibits filament elongation through ADP-Pi- or ADP-actin monomers. Moeover, Latrunculin A does not change the depolymerization rates of ADP- actin filaments or ADP-Pi-actin filaments generated. Previously, Latrunculin A induces striking reversible changes in the morphology of mammalian cells in culture and disrupts the organization of their microfilaments.
To sum up, Latrunculin A binds to actin monomers and inhibits polymerization of actin.