F-actin network-specific sorting of actin binding proteins
In an extremely crowded cytoplasm, cells must simultaneously assemble multiple distinct filamentous actin (F-actin) networks with the proper architecture and dynamics at the correct time and place. How a cell initiates and maintains these distinct F-actin structures to drive essential cellular functions is a fundamental question in cell biology. In cells, actin assembly factors initiate F-actin assembly from monomeric globular actin subunits (G-actin). The organization of these filaments into higher-order networks with specific architectures and dynamics is regulated by the coordinated efforts of actin-binding proteins (ABPs) that nucleate, crosslink, sever, stabilize, and cap actin filaments. Therefore, the accurate localization of particular ABPs to specific F-actin networks is paramount, as the identity of each F-actin network is defined by the subgroup of ABPs with which it associates. However, the mechanistic principles guiding the sorting of ABPs to distinct F-actin networks remain largely unclear:
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Why and how do different ABPs associate with distinct F-actin networks?
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What particular properties of ABPs are important for their sorting?
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What role (if any) does the assembly factor play in setting up ABP sorting?
These types of questions are ideally studied in fission yeast, which has three distinct F-actin networks that are each generated by a unique assembly factor (Figure A). We use both in vivo (yeast genetics, live cell imaging (Movie 1)) and in vitro (single molecule multi-color TIRF microscopy (Movie 2)) methods to determine the mechanisms by which actin binding proteins sort to distinct F-actin networks in cells. Additionally, the emergence of distinct actin filament networks from a shared pool of actin monomers presents an interesting non-equilibrium system. The Kovar Lab uses statistical mechanical and computational methods to understand the theoretical bases governing actin network organization and assembly, particularly through modeling the competitive and cooperative interactions between actin binding proteins.
