Self-organizing motors divide active liquid droplets

Abstract

The cytoskeleton is a collection of protein assemblies that dynamically impose spatial structure in cells and coordinate processes such as cell division and mechanical regulation. Biopolymer filaments, cross-linking proteins, and enzymatically active motor proteins collectively self-organize into various precise cytoskeletal assemblies critical for specific biological functions. An outstanding question is how the precise spatial organization arises from the component macromolecules. We develop a new system to investigate simple physical mechanisms of selforganization in biological assemblies. Using a minimal set of purified proteins, we create droplets of cross-linked biopolymer filaments. Through the addition of enzymatically active motor proteins we construct composite assemblies, evocative of cellular structures such as spindles, where the inherent anisotropy drives motor self-organization and droplet deformation. These results suggest that simple physical principles underlie the self-organization in complex biological assemblies and inform bio-inspired materials design.

Nonlinear dynamics of a chemically-active drop: From steady to chaotic self-propulsion

“…o , and C (1) given by (12), (13), and (A12)-(A16), respectively, into the boundary conditions (A7)-(A9). Since we consider the case of a steady flow, projection of the result onto the n-th Legendre polynomial yields a sequence of sets of homogeneous linear algebraic equations for the constant amplitudes a (1) i,n , a (A17) In essence, condition (A17) establishes that n-th neutrally stable eigenmode of the linearized problem exists at a distinct point Pe = Pe n .…”

“…At the collective level, and similarly to phoretic particles, active droplets can self-organize in complex clusters [10] in the presence of chemically-active species. Multiple active drops "feel" each other's presence and adjust their behavior: they may form ordered clusters [11,12], repel [13], or avoid crossing each other's trails [5]. * sebastien.michelin@ladhyx.polytechnique.fr Experimental observations of active drops typically employ relatively small droplets with radius ∼100 µm or less.…”

Optical Tweezers Approaches for Probing Multiscale Protein Mechanics and Assembly

“…Quantifying and rationalizing the mechanics of proteins at various hierarchical scales is critical in fields including biomaterials design ( Wu et al, 2018 ; Sorushanova et al, 2019 ), neurodegeneration ( Yu et al, 2013 ), active matter ( Koenderink et al, 2009 ; Lansky et al, 2015 ; Weirich et al, 2019 ; Gompper et al, 2020 ), cellular biology – including the rapidly developing field of liquid-liquid phase separation ( Bergeron-Sandoval et al, 2018 ; Jawerth et al, 2018 ; Kaur et al, 2019 ; Shayegan et al, 2019 ; Alshareedah et al, 2020 ), and mechanobiology ( Burla et al, 2019 ; Mathieu and Manneville, 2019 ). Optical tweezers are well suited to probing protein mechanics at scales ranging from single molecules to fibers to networks, and, with the integration of complementary measurement modalities, will continue to deliver new insight into the mechanisms by which mechanical responsiveness is imparted by proteins.…”

Cytoskeletal and Actin‐Based Polymerization Motors and Their Role in Minimal Cell Design

“…[86,87] In addition, vesicles have been designed, in which the cytoskeleton was coupled to the membrane, while the topology of the cytoskeletal network, as well as the contractile activity were modulated. [89] The addition and self-organization of myosin motors lead to droplet deformation and eventually to the formation of spindle like assemblies due to inherent anisotropies. In the context of mimicking cellular functions that could be potentially used toward the bottom-up design of a cell, a minimal set of purified proteins was used to create droplets of cross-linked actin filaments.…”

“…In the context of mimicking cellular functions that could be potentially used toward the bottom-up design of a cell, a minimal set of purified proteins was used to create droplets of cross-linked actin filaments. [89] The addition and self-organization of myosin motors lead to droplet deformation and eventually to the formation of spindle like assemblies due to inherent anisotropies. This example illustrates how artificial design can mimic cell functions that are performed in vivo by other proteins, e.g., by microtubules in the case of most eukaryotic mitotic spindles.…”