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Self-organizing motors divide active liquid droplets
Kimberly L. Weirich, Kinjal Dasbiswas, Thomas A. Witten, Suriyanarayanan Vaikuntanathan, and Margaret L. Gardel
PNAS June 4, 2019 116 (23) 11125-11130; first published May 21, 2019 https://doi.org/10.1073/pnas.1814854116
Kimberly L. Weirich
aJames Franck Institute, University of Chicago, Chicago, IL 60637;bInstitute for Molecular Engineering, University of Chicago, Chicago, IL 60637;
Kinjal Dasbiswas
aJames Franck Institute, University of Chicago, Chicago, IL 60637;cDepartment of Physics, University of California, Merced, CA 95343;
Thomas A. Witten
aJames Franck Institute, University of Chicago, Chicago, IL 60637;dDepartment of Physics, University of Chicago, Chicago, IL 60637;
ORCID record for Thomas A. Witten
Suriyanarayanan Vaikuntanathan
aJames Franck Institute, University of Chicago, Chicago, IL 60637;eDepartment of Chemistry, University of Chicago, Chicago, IL 60637
Margaret L. Gardel
For correspondence: gardel@uchicago.edu
Edited by Andrea J. Liu, University of Pennsylvania, Philadelphia, PA, and approved April 24, 2019 (received for review August 28, 2018)
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Self-organized and shape-changing assemblies are fundamental in living systems. However, in synthetic materials, these features remain elusive to reconstruct. Here, we construct liquid droplets out of biological proteins actin and myosin, which are fundamental cellular materials. Since the proteins form filaments, the droplets have internal structure. This structure leads to the self-organization of the protein components, where myosin finds the center of actin droplets, reminiscent of chromosome alignment in cell division. Myosin also strongly interacts with actin, leading to spontaneous shape change and droplet division. These results suggest physical mechanisms of biological processes, while inspiring strategies for soft materials design.
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 system to investigate simple physical mechanisms of self-organization 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, droplet deformation, and division into two droplets. These results suggest that simple physical principles underlie self-organization in complex biological assemblies and inform bioinspired materials design.
active matter
liquid crystal
actomyosin
tactoids
↵1To whom correspondence may be addressed. Email: gardel{at}uchicago.edu.
Author contributions: K.L.W., K.D., S.V., and M.L.G. designed research; K.L.W. and K.D. performed research; K.L.W., K.D., T.A.W., and S.V. contributed new reagents/analytic tools; K.L.W. and K.D. analyzed data; and K.L.W., K.D., T.A.W., S.V., and M.L.G. wrote the paper.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1814854116/-/DCSupplemental.
Published under the PNAS license.
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Kimberly L. Weirich, Kinjal Dasbiswas, Thomas A. Witten, Suriyanarayanan Vaikuntanathan, Margaret L. Gardel
Proceedings of the National Academy of Sciences Jun 2019, 116 (23) 11125-11130; DOI: 10.1073/pnas.1814854116
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