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Updated: Apr 19, 2026

Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
Published on: May 5, 2022
Electrostatic interactions between the Bni1p Formin FH2 domain and actin influence actin filament nucleation
Joseph L Baker1, Naomi Courtemanche2, Daniel L Parton3
1Department of Chemistry, The University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, USA; Institute for Biophysical Dynamics, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA; James Franck Institute, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA; Computation Institute, The University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, USA.
Abstract:
Formins catalyze nucleation and growth of actin filaments. Here, we study the structure and interactions of actin with the FH2 domain of budding yeast formin Bni1p. We built an all-atom model of the formin dimer on an Oda actin filament 7-mer and studied structural relaxation and interprotein interactions by molecular dynamics simulations. These simulations produced a refined model for the FH2 dimer associated with the barbed end of the filament and showed electrostatic interactions between the formin knob and actin target-binding cleft. Mutations of two formin residues contributing to these interactions (R1423N, K1467L, or both) reduced the interaction energies between the proteins, and in coarse-grained simulations, the formin lost more interprotein contacts with an actin dimer than with an actin 7-mer. Biochemical experiments confirmed a strong influence of these mutations on Bni1p-mediated actin filament nucleation, but not elongation, suggesting that different interactions contribute to these two functions of formins.
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