A Platform for Analyzing Force Sensitivity and Multivalency in Actin Networks

Author

Joseph Theo Levin

Date of Award

2024

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Alushin Laboratory

Abstract

The physical structure and dynamics of cells are supported by micron-scale actin networks with diverse geometries, protein compositions, and mechanical properties. These networks are composed of actin filaments and numerous actin binding proteins (ABPs), many of which engage multiple filaments simultaneously to crosslink them into specific functional architectures. Mechanical force has been shown to modulate the interactions between several ABPs and individual actin filaments, but it is unclear how this phenomenon contributes to the emergent force-responsive functional dynamics of actin networks. In this thesis, I first present our work engineering filament linker complexes and combining them with photo-micropatterning of myosin motor proteins to produce an in vitro reconstitution platform for examining how force impacts the behavior of ABPs within multi-filament assemblies. Our system enables monitoring dozens of actin networks with varying architectures simultaneously using total internal reflection fluorescence microscopy, facilitating detailed dissection of the interplay between force-modulated ABP binding and network geometry. Secondly, I present data applying our system to study a dimeric form of the critical cell-cell adhesion protein α-catenin, a model force-sensitive ABP. We find that myosin forces increase homodimeric α-catenin’s engagement of filament bundles, particularly smaller bundles embedded within networks. This activity is largely abrogated in a force-sensing deficient mutant, whose binding is not increased to the same degree on tensed filament bundles and scales linearly with bundle size. I present our model to explain the relative differences in binding between larger and smaller bundles based on differences in per-filament loads, which could influenceα-catenin’s distribution across actin-myosin networks with varying sizes in cells. I discuss potential further work to substantiate that model and its implications. Finally, I discuss our progress designing and creating a fluorescence based force detection system intended to be embedded in the filament linker complexes we created. Such a setup would enable correlative measurement between ABP binding behavior and tensile forces on bound filament bundles. Collectively the work introduces a new approach for the in vitro analysis of F-actin networks and binding proteins which may prove useful in bridging the gaps between existing in vitro, single molecule and cellular approaches.

Comments

A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirement for the degree of Doctor of Philosophy

Recommended Citation

Levin, Joseph Theo, "A Platform for Analyzing Force Sensitivity and Multivalency in Actin Networks" (2024). Student Theses and Dissertations. 762.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/762