Imagine tiny batteries, not those in our electronic devices but smaller and in our cells, powering the reactions that keep us alive. These “batteries” are called mitochondria, and they’re sometimes nicknamed as the powerhouses of the cell. They’re responsible for producing ATP (adenosine triphosphate), the molecule that fuels numerous actions and reactions in our body—from muscle movement to brain activity.

But what if we could build these powerhouses ourselves and make them simpler than mitochondria? What if synthetic cells could harness this energy to grow, repair, or even communicate and feed each other? These are the groundbreaking questions that motivate us, and from which we departed at the beginning of our research journey.

Let’s first dive into what these synthetic versions of mitochondria are and how they could transform synthetic biology and nanotechnology.

What Are Synthetic Mitochondria?

Our synthetic mitochondria are essentially engineered vesicle structures that mimic the natural mitochondria found in our cells but they are much simpler in structure and components. Their purpose? To recycle ATP and supply metabolic energy, just like natural mitochondria do. We build these synthetic powerhouses from nanometer sized lipid vesicles functioning as organelle-like nanoreactors with a handful of proteins that work together to convert chemical energy into ATP.

How Do the Synthetic Mitochondria Work?

Unlike natural mitochondria that use a process called respiration to produce ATP based on burning, i.e. the oxidation, of nutrients like sugars and fats, we use a simple deamination pathway of only four proteins to form ATP.^1,2 The fuel “arginine” is an amino acid and enters the vesicles through a highly selective “valve” in the membrane, the arginine/ornithine transporter protein. Arginine is burned by deamination. The released energy is transferred stepwise in three enzymatic reactions to finally phosphorylate adenosine diphosphate (ADP) back to ATP. ATP is then exported from the vesicles by a specific transporter protein at the exchange of ADP. Now ATP is available to fuel ATP-dependent reactions outside the vesicle.

The carefully selected membrane proteins are key players to the success of the synthetic mitochondria. In contrast to simple pores they only allow the passage of their specific substrates. They can maintain concentration gradients that are essential for the sustained conversion and the storage of molecular energy.

How Can We Use those Synthetic Mitochondria?

These synthetic mitochondria aren’t just curiosities in a lab—they’re like mini-generators that could one day power synthetic cells or “biological machines.” Imagine a world where engineered cells could be fueled by these synthetic mitochondria, performing specific tasks like synthesizing vital molecules, signaling with specific parts of the cell, or even supporting living cells with more energy.

Synthetic Syntrophy Between Synthetic Cells

We used these energy-producing synthetic mitochondria to feed another type of synthetic cell. These are nanoreactors that consume ATP for the concentration of small molecules. The accumulation of molecules against their natural concentration gradient costs energy. How do the nanoreactors get this energy? By ATP released from the synthetic mitochondria!  The energy-consuming vesicles contain the same ADP/ATP carrier protein but here it is used to import ATP. ATP is then converted to ADP inside the nanoreactors and ADP leaves the vesicles in counter-exchange for fresh ATP. ADP is taken up by the synthetic mitochondria, regenerated and the cycle starts all over again!

We were surprised ourselves how well this cross-feeding works. The performance of the ATP-consuming reactions was much better than anticipated. The most intriguing part to us is that both vesicles really depend on each other and will adapt their ATP production and consumption rates accordingly.

What Is the Potential of Synthetic Mitochondria and Such Nanoreactors?

Creating these processes synthetically is no small feat. Synthetic mitochondria are for sure complex, but compared to their natural counterpart they are still very simple. We see this as an advantage to replicate and understand metabolic processes in a stable and reliable way to be practical.

We foresee that synthetic mitochondria could power life-like processes in synthetic biology and nanotechnology in the future. Here are a few exciting possibilities:

    Feeding synthetic cells: One big challenge in synthetic biology is finding a way to provide a constant energy source for synthetic cells.³ With synthetic mitochondria, researchers could “feed” energy to these cells, enabling them to grow, replicate, and perform tasks.

    Eco-friendly biological machines: Imagine a world where synthetic cells could consume waste materials or produce clean energy. Synthetic mitochondria could supply these machines with the power they need, paving the way for innovative solutions to environmental problems.

    Research on cell processes: By studying synthetic mitochondria, scientists can learn more about how energy regeneration works in living cells. These insights could improve our understanding of health, disease mechanisms (i.e. the derailing of cellular processes), and aging.

The Future of Artificial Powerhouses

Of course, there are challenges in integrating synthetic mitochondria for real-world applications. Cells are like traffic hubs, and making sure each part “talks” to each other correctly is essential for coordinated function, but progress is being made.

Synthetic mitochondria, turning chemical energy into a usable form, will bring us one step closer to integrating biology with engineering, creating life-inspired technologies that could change how we design our future materials out of equilibrium.

With this research ahead, the possibilities for synthetic mitochondria are truly electrifying!

References

(1)         Pols, T.; Singh, S.; Deelman-Driessen, C.; Gaastra, B. F.; Poolman, B. Enzymology of the Pathway for ATP Production by Arginine Breakdown. FEBS J. 2021, 288 (1), 293–309. https://doi.org/10.1111/febs.15337.

(2)         Pols, T.; Sikkema, H. R.; Gaastra, B. F.; Frallicciardi, J.; Śmigiel, W. M.; Singh, S.; Poolman, B. A Synthetic Metabolic Network for Physicochemical Homeostasis. Nat. Commun. 2019, 10 (1), 4239. https://doi.org/10.1038/s41467-019-12287-2.

(3)         Adamala, K. P.; Dogterom, M.; Elani, Y.; Schwille, P.; Takinoue, M.; Tang, T.-Y. D. Present and Future of Synthetic Cell Development. Nat. Rev. Mol. Cell Biol. 2023. https://doi.org/10.1038/s41580-023-00686-9.