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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.
[1] [2] [3] In most eukaryotic cells lacking a cell wall, the cortex is an actin-rich network consisting of F-actin filaments, myosin motors, and actin-binding proteins. [ 4 ] [ 5 ] The actomyosin cortex is attached to the cell membrane via membrane-anchoring proteins called ERM proteins that plays a central role in cell shape control.
This is highly dependent on the blue light receptor phototropin and the actin cytoskeleton, as actin bundles are seen to form along the anticlinal wall in blue light. [6] A protein called ANGUSTIFOLIA was also recently discovered to regulate nucleus movement in the dark by forming a complex that adjusts the alignment of actin filaments. [7]
Profilin is an actin-binding protein involved in the dynamic turnover and reconstruction of the actin cytoskeleton. [1] It is found in most eukaryotic organisms. Profilin is important for spatially and temporally controlled growth of actin microfilaments, which is an essential process in cellular locomotion and cell shape changes.
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.
The actin polymers then push the membrane as they grow, forming the pseudopod. The pseudopodium can then adhere to a surface via its adhesion proteins (e.g. integrins), and then pull the cell's body forward via contraction of an actin-myosin complex in the pseudopod. [9] [10] This type of locomotion is called amoeboid movement.
Cell migration could be affected in some pathological states. For example, in conditions of high lipoperoxidation, actin has been shown to be post-translationally modified by the lipoperoxidation product 4-hydroxynonenal (4-HNE). [43] This modification prevents the remodelling of the actin cytoskeleton, which is essential for cell motility.
Together with an alpha-beta catenin complex, the cadherin can bind to the microfilaments of the cytoskeleton of the cell. This allows for homophilic cell–cell adhesion. [18] The β-catenin–α-catenin linked complex at the adherens junctions allows for the formation of a dynamic link to the actin cytoskeleton. [19]