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Their formation and turnover are regulated by many proteins, including: [citation needed] Filament end-tracking protein (e.g., formins, VASP, N-WASP) Filament-nucleator known as the Actin-Related Protein-2/3 (or Arp2/3) complex; Filament cross-linkers (e.g., α-actinin, fascin, and fimbrin) Actin monomer-binding proteins profilin and thymosin β4
Microfilament Polymerization. Microfilament polymerization is divided into three steps. The nucleation step is the first step, and it is the rate limiting and slowest step of the process. Elongation is the next step in this process, and it is the rapid addition of actin monomers at both the plus and minus end of the microfilament.
The oligomerization is the rate-determining step, considering actin filament formation as a whole. The so-called lag phase of actin polymerization originates from this step. It takes quite a while until polymerization starts, but once it has, the process is autocatalytic until the physiological maximum of the polymerization rate is reached.
The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton.
Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils.It is found in essentially all eukaryotic cells, where it may be present at a concentration of over 100 μM; its mass is roughly 42 kDa, with a diameter of 4 to 7 nm.
Cytochalasins are fungal metabolites that have the ability to bind to actin filaments and block polymerization and the elongation of actin. As a result of the inhibition of actin polymerization, cytochalasins can change cellular morphology, inhibit cellular processes such as cell division, and even cause cells to undergo apoptosis. [1]
The C protein plays an important role in the retrograde transport of vesicles and is also known as cytoplasmic dynein. MAP-2 proteins are located in the dendrites and in the body of neurons, where they bind with other cytoskeletal filaments. The MAP-4 proteins are found in the majority of cells and stabilize microtubules.
Within the lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia. [2] The lamellipodium is born of actin nucleation in the plasma membrane of the cell [1] and is the primary area of actin incorporation or microfilament formation of the cell.