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Cell surface (cortical) actin remodeling is a cyclic (9-step) process where each step is directly responsive to a cell signaling mechanism. Over the course of the cycle, actin begins as a monomer, elongates into a polymer with the help of attached actin-binding-proteins, and disassembles back into a monomer so the remodeling cycle may commence again.
The nucleation of new actin filaments – the rate-limiting step in actin polymerization – is aided by actin-nucleating proteins such as formins (like formin-2) and the Arp2/3 complex. [118] Formins help to nucleate long actin filaments. They bind two free actin-ATP molecules, bringing them together.
This complex then binds to actin, leading to polymerization. For actin polymerization through the cadherin pathway, proteins of the Rho GTPases family are also involved. This complex is regulated by phosphorylation, which leads to downregulation of adhesion. Several factors can induce the phosphorylation, like EGF, HGF or v-Src. The cadherin ...
Cytoplasmic streaming occurs due to the motion of organelles attached to actin filaments via myosin motor proteins. [8] However, in Chara corallina, the organization of actin filaments is highly ordered. Actin is a polar molecule, which means that myosin only moves in one direction along the actin filament. [3]
Actin polymerization can further be regulated by profilin and cofilin. [6] Cofilin functions by binding to ADP-actin on the negative end of the filament, destabilizing it, and inducing depolymerization. Profilin induces ATP binding to G-actin so that it can be incorporated onto the positive end of the filament.
RMD, which are type II formins, consist of a phosphatase, (PTEN)-like domain (responsible for protein localization), and FH1 and FH2 domains (promotes actin polymerization). [ 43 ] [ 44 ] [ 42 ] In order to discover the localization of RMD in the pollen tube, transient assays of growing pollen tubes of tobacco was performed and the fluorescent ...
Cofilin is a ubiquitous actin-binding factor required for the reorganization of actin filaments. ADF/Cofilin family members bind G-actin monomers and depolymerize actin filaments through two mechanisms: severing [11] and increasing the off-rate for actin monomers from the pointed end. [12] "Older" ADP/ADP-Pi actin filaments free of tropomyosin ...
The following steps describe one force-generating cycle of an actoclampin molecular motor: The polymerization cofactor profilin and the ATP·actin combine to form a profilin-ATP-actin complex that then binds to the end-tracking unit; The cofactor and monomer are transferred to the barbed-end of an actin already clamped filament