Protein factories: Using the power of evolution to defeat the enemy

Evolution has played a vital role in the billions of years of development of life. It is a great natural force that scientists hope to simulate in the laboratory.

The winners of the 2018 Nobel Prize in Chemistry are two American scientists and one British scientist. When the Nobel Prize Committee first announced the award, it told everyone with affectionate and poetic words that the three winners won the award for "harnessing the power of evolution."

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Frances Arnold, an American female scientist and professor at the California Institute of Technology, received half of the award for her pioneering work in the field of directed evolution. Directed evolution simulates the process of evolution artificially to induce changes in the structure of biological molecules such as proteins so that they can achieve specific functions. It is worth mentioning that she is the fifth woman to win the Nobel Prize in Chemistry.

American scientist George Smith and British scientist Gregory Winter shared the other half of the award for their contributions to phage display technology, which has become an important tool for drug development.

The essence of the two groups of award-winning results is to use the inherent physiological process in biological cells to achieve specific application purposes. This physiological process is the synthesis of proteins by cells under the control of genes. It is a biochemical process that never stops in organisms. So, how do these three scientists use the power of directed evolution technology to control billions of tiny molecules and benefit the world?

The word "evolution" represents an upward and forward trend. When it comes to specific species, it means becoming faster, taller, stronger, smarter, or having a stronger tolerance to certain adverse conditions. However, the internal driving force of the evolution of organisms is often the evolution of certain proteins in the cells that make up the organisms. These evolved proteins require mutated genes to express them. In professional terms of biology, after a gene mutates, the protein expressed by the gene will also change. In other words, the evolution of proteins is actually the natural result of gene mutation.

Directed evolution is a process of rapidly evolving proteins in the laboratory

For example, during the long evolution process, the koalas in Australia have developed the habit of eating eucalyptus leaves as their main food, and eucalyptus leaves can produce terpenes, a toxic substance that kills most animals. However, the genes related to terpene resistance are highly expressed in koalas, so that the koalas' kidneys can process terpenes into water-soluble substances and excrete them out of the body. The strong kidney function of koalas is due to the continuous strengthening of the functions of various enzymes used to decompose terpenes during the long evolution process.

The fundamental idea of ​​directed evolution is to mutate and eliminate proteins repeatedly under artificial conditions, so as to selectively produce the desired proteins. Specifically, first, DNA synthesis technology is used to establish a variant group containing a variety of base sequences (which can be considered a DNA library), and then these DNAs are used to transcribe proteins corresponding to their structures, so that a protein library containing a variety of proteins can be formed. When these proteins achieve the specific goals we set, they must have different functions, and then the best ones are selected. It is like in the product development process, the poor solutions are eliminated and only the excellent molecules are retained.

At this point, the fun has just begun. After scientists have selected a good protein, they will perform the reverse process of the above process again, determine the DNA structure corresponding to the transcription of the protein, and then use the very mature PCR technology (PCR technology is a molecular biology technology that simulates the natural replication process of DNA in the body and amplifies DNA molecules in vitro) to replicate the DNA in large quantities. Moreover, during this replication process, appropriate mutations may be introduced at the same time in order to further improve the performance of the protein. After this series of operations are completed, the protein's leap evolution can be completed in a very short time.

Enzymes are proteins that can realize certain specific biochemical processes in organisms (also known as biological enzymes, proteases, etc.). Enzymes are certain special proteins (very few are RNA or DNA) produced by living cells. They participate in a series of biochemical reactions in organisms and regulate the rate, direction and degree of reactions through complex and sophisticated mechanisms. They can be called "magicians" in organisms. In the human body, enzymes are usually synthesized directly in cells based on the genetic information recorded by genes.

Enzymes are proteins that often have unparalleled efficiency and ability in solving certain specific problems. Their functions are so fascinating that humans not only want to understand their operating principles, but also want to obtain them in large quantities for their own use. In fact, artificially prepared enzymes have been widely used in the production of detergents, treatment of crude oil pollution, preparation of biomass fuels, killing of harmful bacteria and other fields. And evolutionary control technology is an excellent tool for mass production of artificial enzymes.

What are the functions of artificial enzymes?

Some enzymes synthesized by humans are already able to catalyze some chemical reactions with great application potential. For example, in the reactions of converting carbon dioxide in the atmosphere into organic molecules for fuel and combining nitrogen and hydrogen in the atmosphere to synthesize ammonia, the catalytic efficiency of synthetic proteins is comparable to that of inorganic catalysts.

Many East Asians lack lactose hydrolase in their bodies, which can cause discomfort such as flatulence and diarrhea after drinking milk. However, adding artificial lactose hydrolase to various milks can greatly alleviate the discomfort after drinking milk.

In addition, the application of artificial enzymes also includes disease treatment. For example, artificial enzymes are expected to help patients with intestinal diseases break down gluten in the stomach, thereby reducing intestinal pressure.