Biology Reference
In-Depth Information
SOME OPEN QUESTIONS AND FUTURE PERSPECTIVES
In this chapter we have shown a possible (and realistic) experimental approach to the
construction of minimal cells in the laboratory. We also gave a broad overview of the
current state of the art in this field, from three different viewpoints: (1) the
reconstruction of genetic/metabolic networks inside lipid vesicles for achieving minimal
living entities; (2) the importance of physical effects for the material construction of
minimal cells, in particular the physics of solute entrapment; and (3) the technological
viewpoint, that will certainly affect the future developments of SSMCs in the
biotechnology field.
Within the viewpoint (1), we have seen that genes can be expressed inside lipid vesicles. In
the case of water-soluble proteins, their intravesicle synthesis should be considered a viable
route for developing biochemical functions, except for the case of proteins that require post-
translational modifications. In the case of lipid-associated proteins, instead, results indicate
that careful design of the membrane composition is a prerequisite for their successful
production. Note that by varying the chemical nature of lipids, side problems might arise
with respect to encapsulation efficiency and chemical interference with the transcription/
translation kits.
One of the most relevant and ambitious open questions in SSMCs research is the
achievement of complete
self-reproduction. In particular, in order to self-
reproduce all its components, as required by the autopoietic theory, minimal cells should
be able to synthesize lipids (for membrane growth), and also synthesize all macromolecular
components that are enclosed in the shell. These two production processes should be
synchronized, in order to let minimal cells grow harmoniously. An unbalanced growth
would be deleterious for self-reproduction. The achievement of synchronized core-and-shell
self-reproduction will help to understand what the physicochemical constraints that regulate
that process are, and possibly, how primitive cells could have faced this problem with a
metabolic network of minimal complexity.
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core-and-shell
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From the viewpoint of solute entrapment (2), we have described a novel and unexpected
behavior that brings about the spontaneous formation of solute-filled compartments, even
starting from diluted solution. We have already discussed the relevance of such observation
for understanding the origin of cellular life. An open question in this respect is certainly
linked to the investigation of the mechanism that originates these special vesicles. This
could not only explain the origin of cellularity, but also could allow the formation of
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vesicles in a controlled manner (the production of enzyme-filled
vesicles could find applications in enzyme therapy). Additional questions are related to the
extension of the results obtained to other proteins and other lipids, to verify the generality
of the mechanism. An interesting scenario, which is currently under study in our laboratory,
focuses on the exploitation of the spontaneous concentration of solutes inside lipid vesicles
to activate an otherwise sluggish reaction (e.g. a diluted mixture of compounds that does
not react in bulk solution
super-concentrated
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due to the low concentration
becomes concentrated, and
reacts, only inside lipid vesicles).
Several open questions and perspectives are instead related to the biotechnology issues
(3), because this field is still in its infancy. The first one is about the goal of standardizing
SSMC production. Only when this target is reached will synthetic cells (non-
cells)
enter the applicative phase. In addition to the already presented example of intelligent and
programmable drug-producing vectors, SSMCs could be used for in vitro assays on cell-like
systems, as biosensors, as microrepairing devices, for multienzyme immobilization, or to
study cellular function without the interference of background processes. It is remarkable
that the employment of SSMCs in human health and medicine is advantageous because
they should not present biosafety issues, in contrast to engineered living cells.
living
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