Abstract
The actin cytoskeleton mediates mechanical coupling between cells and their tissue microenvironments. The architecture and composition of actin networks are modulated by force; however, it is unclear how interactions between actin filaments (F-actin) and associated proteins are mechanically regulated. Here we employ both optical trapping and biochemical reconstitution with myosin motor proteins to show single piconewton forces applied solely to F-actin enhance binding by the human version of the essential cell-cell adhesion protein αE-catenin but not its homolog vinculin. Cryo-electron microscopy structures of both proteins bound to F-actin reveal unique rearrangements that facilitate their flexible C-termini refolding to engage distinct interfaces. Truncating α-catenin's C-terminus eliminates force-activated F-actin binding, and addition of this motif to vinculin confers force-activated binding, demonstrating that α-catenin's C-terminus is a modular detector of F-actin tension. Our studies establish that piconewton force on F-actin can enhance partner binding, which we propose mechanically regulates cellular adhesion through α-catenin.
Highlights
Cells probe and respond to the mechanical properties of their surroundings through cytoskeletal networks composed of actin filaments (F-actin), myosin motor proteins, and dozens of actin-binding proteins (ABPs)
Filamentous actin (F-actin) has been reported to adopt a structural landscape of co-existing conformations in cryo-electron microscopy studies (Galkin et al, 2010b), leading to speculation that actin filaments could themselves serve as tension sensors by presenting distinct binding interfaces to ABPs in the presence of load (Galkin et al, 2012)
Utilizing a novel Total Internal Reflection Fluorescence (TIRF) microscopy in vitro reconstitution assay, we further show that physiological forces generated by myosin motor proteins activate a-catenin F-actin binding
Summary
Cells probe and respond to the mechanical properties of their surroundings through cytoskeletal networks composed of actin filaments (F-actin), myosin motor proteins, and dozens of actin-binding proteins (ABPs). These networks transmit forces through cell-matrix focal adhesions (Humphrey et al, 2014) and cell-cell adherens junctions (Charras and Yap, 2018), plasma membrane-associated manyprotein assemblies which serve as hubs for the conversion of mechanical cues and stimuli into biochemical signaling cascades (“mechanotransduction”). To our knowledge, direct observation of enhanced F-actin binding by ABPs when force is applied solely to the filament (which we here refer to as “force-activated binding”) has never been reported, and structural mechanisms enabling ABPs to detect force on F-actin are unknown
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