An Enzymatic Modular System Makes Amino Acids from Methanol 

Amino acids are critical macronutrients, showing up in food additives and dietary supplements. However, they are currently not very sustainable to produce. Most amino acids are made by fermentation, which requires large amounts of soybeans or other feedstock that need considerable amounts of land and water to grow initially.

In contrast, making amino acids directly from chemical starting products, like methanol, offers a less agriculturally intensive alternative. Additionally, since methanol can be produced from carbon dioxide, a potent greenhouse gas, synthesizing amino acids from this single-carbon alcohol has the potential to address multiple sustainability issues at once.

Volker Sieber, a synthetic biologist at the Technical University of Munich, focuses on developing these types of processes. He and his group previously synthesized alanine using methanol made from carbon dioxide.¹ With this success, Sieber said, “We wanted to see whether we could extend this to the other building blocks of the proteins.”

In a study published in Nature Communications, Sieber and his team developed a modular cascade of enzymatic pathways to produce six amino acids.² This process, conducted with free enzymes, sets the stage for more sustainable amino acid production. Although the study is still on a small scale, Donald Wellings, the founder and managing director of the biotechnology group SpheriTech and who was not involved in the study, said, “The ideas that they have are really quite progressive.”

The researchers’ goal was to create a flexible system to produce six amino acids of varying sizes—glycine, serine, L-aspartic acid, L-valine, L-glutamic acid, and L-proline—from methanol as a proof of concept. The first step to synthesizing these molecules from the single-carbon alcohol was to convert it into either a two-carbon compound, glycoaldehyde, or a three-carbon compound, dihydroxyacetone. Using different enzymes in this initial reaction, Sieber and his team controlled the ratios of these two precursors that then influenced which amino acids could be made.

From here, Sieber’s team reverse-engineered their system from their end products. They used available databases and tools to identify pathways and enzymes from different metabolic systems that could produce either the desired amino acids or the necessary intermediates for them in an energy efficient reaction. “The pathways [the PhD students] came up with are partially non-natural. So, the enzymes come from very different organisms and are put together to then have this conversion,” Sieber said.

Ultimately, the researchers created a workflow of three modules: the first converts methanol into glycoaldehyde, dihydroxyacetone, or a combination of the two; the second consists of intermediate reactions that produce important cofactors alongside the metabolites; and the third that finally synthesizes the amino acids with the help of the generated cofactors. Because some of the compounds, like methanol, are toxic to living cells, the team kept the cascade as a cell-free system.

Putting their specially-designed system to the test, the researchers successfully produced each of the six amino acids. However, while some reactions led to high yields, like the team achieving a 91 percent conversion to glycine, others had much lower yields. The researchers only achieved a 46 percent yield for the synthesis of L-glutamic acid. Sieber said that he and his team will be exploring how to optimize their system to improve the output of amino acids.

Wellings said that the approach is clever. “There's no real great shortage of amino acids at the moment worldwide, but it's always worth looking at alternative routes,” he said. He noted, though, that producing the amino acids in a cell-free system makes it more difficult to purify them from the enzymes also in suspension; he said that the researchers could consider immobilizing them to address this problem.

Wellings also remarked that since many of the enzymes that are used in the cascade aren’t currently commercially produced, the team will need to consider how to scale up their production alongside their amino acid synthesis. Broadly, Wellings said that the approach was “on the right track” for addressing sustainability in amino acid production. “It does show the potential for the future,” he said.

Considering the decades headstart that existing fermentation technologies have had, Sieber remains optimistic in his team’s approach. “Overall, I believe that the enzymes can be engineered quite efficiently, much more easily than whole microorganisms,” he said.