Light-controlled adhesion and dynamic processes in lipid vesicles
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Abstract
The aim of bottom-up synthetic biology is to use molecular building blocks to create synthetic cells and to mimic cell functions. In biological cells, many of their cellular functions arise directly from both the spatial and temporal control of fundamental processes. Examples of these controlled events are the formation of protein patterns at the cellular and multicellular scale and cell adhesion during motility and tissue development. When mimicking these functions in minimal synthetic cells, visible light can be used as a trigger to provide the required high spatiotemporal control with the added advantage of it being non-invasive, biocompatible and dynamic.
Dynamic protein patterns are fundamental in cell signaling, cell division, cell migration, and tissue formation and are tightly regulated. To replicate and control the formation of protein patterns in a minimal synthetic cell, I used the light switchable protein dimer iLID, which interacts with its binding partners Micro or Nano under blue light conditions and dissociates from them in the dark. For this purpose, iLID was immobilized on giant unilaminar vesicles (GUVs), which were used as a minimal cell model. Illuminating these GUVs with blue light leads to the recruitment of a Nano fused proteins of interest and their subsequent dissociation when the light trigger is turned off. The iLID-Nano interaction allowed for the patterning proteins over multiple cycles and on different scales, from sub-GUV level to a single vesicle and to tissue-like GUV assemblies.
During cell motility, the cell adheres asymmetrically to a surface with new adhesions forming at the front and adhesions that dissemble at the back. The iLID-Micro dimer was used to imitate motility in a minimal synthetic cell through the light-guided movement of GUVs. This was achieved by controlling adhesions both at the subcellular scale and over time with light. For this purpose, iLID was immobilized on a glass surface to mimic the extracellular matrix with Micro attached to a GUV to mimic the cell adhesion receptor. The iLID-Micro interaction was strong enough to induce GUV adhesion to the surface under blue light, which reversed in the dark, as witnessed by the changing adhesion energies and length of adhesion site. The high spatiotemporal control of light was used to create stronger adhesion in areas exposed to light and weaker adhesions in areas left in the dark. This asymmetry in adhesion led to movement of the vesicle towards the illuminated regions in a manner similar to cell migration. Displacement of the GUV over multiple cycles at a speed close to that seen in mammalian cell motility allowed guiding the GUV over tens of micrometers in different directions.
The interaction between cells through their adhesion is important for the building of larger tissues from single cells, for the organization of cells within their environment, and for communication between them. The blue light dependent interaction of iLID and Nano was employed to control cell-cell adhesions between two populations of GUVs functionalized with these proteins respectively. When mixed together in close proximity, blue light illumination triggered the adhesion of the different subpopulations of vesicles. The interaction was strong enough that the adhered vesicles withstood mechanical stresses like laminar flow, but not strong enough to induce fusion of the lipid bilayers.
Overall, the blue light triggered interaction of iLID with Micro and Nano, is a valuable new tool in bottom-up synthetic biology for mimicking cell functions where dynamic control in time and space is required. Not only does it provide a general way to pattern proteins of interest and control interactions between different minimal cells but it also allows for reproducing the dynamic asymmetry in adhesion observed during cell motility and guiding the movement of a vesicle with visible light.