Mooren OL, McConnell P, DeBrecht JD, Jaysingh A, Cooper JA. Reconstitution of Arp2/3-nucleated actin assembly with proteins CP, V-1, and CARMIL.
Curr Biol 2024:S0960-9822(24)01292-2. [PMID:
39437783 DOI:
10.1016/j.cub.2024.09.051]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 08/30/2024] [Accepted: 09/19/2024] [Indexed: 10/25/2024]
Abstract
Actin polymerization is often associated with membrane proteins containing capping-protein-interacting (CPI) motifs, such as capping protein, Arp2/3, myosin I linker (CARMIL), CD2AP, and WASHCAP/Fam21. CPI motifs bind directly to actin-capping protein (CP), and this interaction weakens the binding of CP to barbed ends of actin filaments, lessening the ability of CP to functionally cap those ends. The protein V-1/myotrophin binds to the F-actin-binding site on CP and sterically blocks CP from binding barbed ends. CPI-motif proteins also weaken the binding between V-1 and CP, which decreases the inhibitory effects of V-1, thereby freeing CP to cap barbed ends. Here, we address the question of whether CPI-motif proteins on a surface analogous to a membrane lead to net activation or inhibition of actin assembly nucleated by Arp2/3 complex. Using reconstitution with purified components, we discovered that CARMIL at the surface promotes and enhances actin assembly, countering the inhibitory effects of V-1 and thus activating CP. The reconstitution involves the presence of an Arp2/3 activator on the surface, along with Arp2/3 complex, V-1, CP, profilin, and actin monomers in solution, recreating key features of cell physiology.
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