The cells that make up all living things are in constant interaction with their environment. Most cells perform complex chemical processes to ensure the cell and the organism remain healthy. Scientists have not yet been able to replicate a fully-functional synthetic cell, but it now appears they are off to a good start. A team of biophysicists have developed basic artificial vesicles capable of changing shape and moving spontaneously.
The vesicles created in this study will be used in future design of increasingly-complex artificial cellular structures, capable of interacting with the environment and carrying out the same processes as a natural biological cell. The research was led by Andreas Bausch from Technische Universität München, and the paper appeared on the cover of Science.
Bausch’s team went back to the basics of cell biology and used biomolecules to build the most fundamental cellular structures from the protein level up. A rudimentary cytoskeleton was constructed by adding tiny tube-shaped polymers called microtubules inside the lipid bilayer membrane that served as the vesicle’s casing. Proteins called kinesins were also added to push along the microtubules, providing movement. Kinesins require coenzyme adenosine triphosphate (ATP) to function, which was added as a source of fuel.
Within the vesicle, the microtubules formed a constantly moving flat layer of liquid crystal. Liquid crystal is a state of matter that is neither liquid nor solid, yet has properties similar to both states.
"One can picture the liquid crystal layer as tree logs drifting on the surface of a lake," lead author Felix Keber said in a press release. "When it becomes too congested, they line up in parallel but can still drift alongside each other.”
As the 2D arrangement of the microtubule liquid crystals are trying to completely line a 3D spheroid, it cannot be done flawlessly. Think of it like trying to gift wrap a basketball. The paper can pressed mostly flat, but eventually there will be unavoidable creases and faults. The faults within the microtubules caused some to be packed in a different orientation to fit in.
The microtubule faults had not impacted the shape or integrity of the vesicle under normal circumstances, but that changed when the vesicles were subjected to different environmental conditions. As water was extracted from the vesicle due to osmosis, the bilayer membrane deflated. Movement from the microtubules in the faults caused the sagging membrane to adopt new shapes, including some with spike-like protrusions.
"With our synthetic biomolecular model we have created a novel option for developing minimal cell models," Bausch states. "It is ideally suited to increasing the complexity in a modular fashion in order to reconstruct cellular processes like cell migration or cell division in a controlled manner. That the artificially created system can be comprehensively described from a physical perspective gives us hope that in the next steps we will also be able to uncover the basic principles behind the manifold cell deformations."