Coordination of actin plus-end dynamics by IQGAP1, formin, and capping protein

Abstract

Cell processes require precise regulation of actin polymerization at filament plus ends to execute normal functions. The detailed mechanisms used to control filament assembly at plus ends in the presence of diverse and often opposing regulators is not clear. Here we explore and identify residues important for the plus-end related activities of IQGAP1. In multi-wavelength TIRF assays, we directly visualize dimers of IQGAP1, mDia1, and capping protein (CP) on filament ends alone and as a multicomponent end binding complex. IQGAP1 promotes the turnover of end-binding proteins, reducing the dwell times of CP, mDia1, or mDia1-CP "decision complexes" by 8-18-fold. Loss of these activities in cells disrupts actin filament arrays, morphology, and migration. Together, our results reveal a new role for IQGAP1 in promoting protein turnover on filament ends and provide new insights into how actin assembly is regulated in cells.

Cyclase-associated protein interacts with actin filament barbed ends to promote depolymerization and formin displacement

“…As a second test of CAP1 interactions with barbed ends, we asked whether CAP1 reduces the duration of formin processive attachment at the barbed end, similar to the recently described effects of capping protein and twinfilin ( 8 , 10 , 11 , 76 , 77 ). A competitive relationship between CAP and formins is predicted by structural modeling, as there is a clash between the CARP domain of CAP and the formin FH2 domain at the penultimate actin subunit of the barbed end ( Fig.…”

“…Capping protein also uses its tentacles to compete with and displace WH2 domains of WASP/WAVE family proteins ( 31 ). Formin-binding partners like Spire and IQGAP1 promote formin recruitment and turnover at barbed ends ( 33 , 76 ). Twinfilin promotes formin displacement from barbed ends and promotes depolymerization of ADP-Pi-actin ( 10 , 36 ) but also binds to capping protein using its capping protein interaction motif to antagonize other capping protein interaction–containing ligands like CARMIL ( 89 ).…”

Uncovering the molecular interactions underlying MBD2 and MBD3 phase separation

“…Cells were grown to 80% confluency and transfected with 100 ng/uL of either plasmid using Lipofectamine 3000 per manufacturer’s instructions in DMEM. The transfection efficiency normally achieved for these cells is 70-99% by immunofluorescence (34). Live-cells were imaged in phenol-red free DMEM (supplemented as above) buffered with 10 mM HEPES (pH 7.4) at 37°C.…”