Aarhus University, Denmark
Among the key molecular mechanisms that make up a cell, receptors and signaling cascades are foundational. It is these mechanisms that allow a cell in nature to receive communication from the outside environment and react to it. In our work, we reconstruct this behavior through the design of artificial receptors whereby signal transduction through sealed biomolecular membranes is achieved using tools of chemistry. We also engineer synthetic, chemical zymogens and couple these up in artificial signaling cascades. Together, artificial receptors and synthetic enzymatic cascades reconstitute the key molecular mechanisms that make up a responsive cell in a multi-cell environment.
University of Bristol, United Kingdom
Living cells are smart autonomic machines that can recognise, sort and process complex molecular cues and respond to their environmental changes to exhibit higher order functionalities such as metabolism, growth, division, motility etc. Construction of synthetic cells/protocells integrated with biomimetic functions such as membrane gating, molecular crowding and spatially controlled enzyme cascades driven chemical signal processing are providing opportunities to engineer non-living materials with life-like properties.
Herein we have designed complex coacervate droplets (protocells) derived from non-covalent interactions between oppositely charged polyelectrolytes and nucleotide that mimic a molecularly crowded interiors within cells. Significantly, these membrane free protocells can sequester high concentrations of range of biotic and abiotic functional molecules and therefore can be employed as programable protocells to achieve bioinspired functions. We show that the highly ordered microarrays of the coacervates installed with wide range of multi-enzyme cascades can receive, sort and process input chemical signals to execute range of Boolean logic functions. Significantly, the protocell-based Boolean logic operations were further advanced by establishing communication between the spatially separated populations of coacervates. Such collective information processing gives rise to opportunities to create feedback loops for programmable output generation. We envisage that protocell-based logic gates will provide opportunities to construct complex biocomputing devices for rapid diagnostics and clinical applications.
Imperial College London, United Kingdom
The development of new sense-and-response systems in synthetic cells (SynCells) is essential to couple the increasingly advanced functions of current cell designs to user-specific environmental cues. Such sense-and-response processes will enable SynCells to function in the complex chemical environments typically encountered by organisms.
In this talk I will discuss how to construct synthetic cells that can respond to their environment by utilising a modular approach which incorporates chemical, biochemical and biophysical motifs into lipid vesicle compartments. Combining vesicle modules across different length scales enables the creation of membrane and membrane-less multicompartment SynCells capable of responding to a variety of local and applied stimuli.
I will highlight the versatility of this approach by presenting different cell designs that incorporate calcium-responsive signalling pathways, light-responsive biocatalysis and motile cells that can travel down a chemical gradient. Such functions could underpin the development of next generation biomimetic devices that function in sense-and-response applications including cell-cell communication, in vivo chemical synthesis and drug delivery.
References:  J. W. Hindley et al., Proc. Natl. Acad. Sci., 2019, 116, 16711–16716.  J. W. Hindley et al., Nat. Commun., 2018, 9, 1093.  S. Zhang et al., Nat. Commun., 2021, 12, 1673.
Aarhus University, Denmark
Signal transduction across lipid bilayers plays the central role in communication in biological systems. In nature, the signals are processed by transmembrane protein receptors. In our work, we aimed to develop artificial receptors that enable the transfer of biological signals across a membrane to give a biological output – using the tools of chemistry. The chemical receptor design was inspired from the field of prodrug design whereby triggered activation leads to drug release. We adapt this methodology to the membrane bound molecules such that activation is exofacial, mimicking the ligand-receptor binding event in natural receptors. Key to the receptor design is that the activation will ensue spontaneous decomposition of the receptor molecule followed by the immediate release of a secondary messenger with the capacity of inducing endofacial enzyme activation. The optimized synthesis of the artificial receptor allows for a scalable production as well as multiple mechanisms of exofacial receptor activation. In the field of artificial receptors, our receptor design brings a novel signaling cascade mechanism, enabling the signal transduction across lipid bilayers to afford enzyme activation, as is the hallmark of activity by natural signaling receptors.
Max Planck Institute for Medical Research, Germany
Extracellular vesicles (EVs) play an important role in intercellular communication, allowing cells to exchange nucleic acid and proteins. They regulate plenty of cellular processes, especially those involved in immune signaling. However, our knowledge about the mechanistic underlying the biophysical principles of EV-based communication is still incomprehensive.
In this work, we investigate vesicle-induced receptor sequestration (VIRS) as a universal mechanism to increase the signaling potency of proteins presented on EV-membranes. To this end, we applied bottom-up synthetic biology principles to assemble fully synthetic EVs. By immobilizing of the receptor ligands FasL and RANK on EV-like vesicles, we show that it increases their signaling potential by more than 100-fold. To compare receptor activation between soluble and EV-presented proteins we perform diffusion simulations within immunological synapses proposing a vesicle-induced local concentration of membrane receptors as the principle structural mechanism underlying EV-based protein presentation. Our assumption is, that EVs serve as extracellular templates encouraging a local aggregation of cell membrane proteins at the EV contact site. This promotes inter-protein interactions which might be potentially universal mechanism explaining the unique structural profit of EV-based intercellular signaling.
University of Oxford, United Kingdom
Synthetic cells are aqueous components enclosed by lipids. There is great interest in establishing communication in synthetic cells by signal diffusion. Many innovative strategies have been developed to control the diffusion rate across bilayers separating synthetic cells .
We present an alternate mechanism for signalling – the use of membrane potential to drive signal entry across synthetic cells. We demonstrate translocation of biopolymer signals across bilayers embedded with channel proteins, and show that signalling rate can be controlled both by the charge density within the protein and the membrane potential.
We engineered methods for synthetic cells to respond to translocated signals. For example, the signal molecule can activate gene transcription by completing a promoter, allowing synthesis of functional proteins in the presence of in vitro transcription translation mix. We show that the same signal can lead to different responses in different synthetic cells.
We aim to incorporate this technology in synthetic tissues where cells sense and response collectively to their environment, with potential applications in nanotechnology and medicine .
References: . Smith, J. M., Chowdhry, R. & Booth, M. J. Controlling Synthetic Cell-Cell Communication. Front. Mol. Biosci. 8, 1321 (2022). . Booth, M. J., Restrepo Schild, V., Downs, F. G. & Bayley, H. Functional aqueous droplet networks. Mol. Biosyst. 13, 1658–1691 (2017).