Enzymes evolved to function efficiently at low temperatures

Scientists have made new discoveries about how enzymes evolved to work well at low temperatures. Enzymes are proteins that help speed up chemical reactions in cells. Each enzyme has a specific temperature range where it works best. For humans, this is around 37 °C. Some organisms, like certain bacteria, thrive in extreme conditions, such as hot springs or icy waters. These extremophiles have enzymes that function in these harsh environments. For example, enzymes from heat-loving organisms work well in high temperatures but struggle at lower ones. In contrast, enzymes from organisms that live in cooler environments are active at lower temperatures. Research suggests that the first life forms on Earth were heat-loving organisms. As the planet cooled down, these organisms adapted to function at cooler temperatures. However, the exact details behind this adaptation are not fully understood. Understanding how these enzymes evolved could help scientists develop new enzymes for various uses, especially in biotechnology. To study the evolution of these enzymes, scientists used a method called ancestral sequence reconstruction (ASR). This technique helps infer sequences of extinct proteins based on those of related living species. A research team from Waseda University, Japan, led by Professor Satoshi Akanuma, focused on a specific enzyme called 3-Isopropylmalate dehydrogenase (IPMDH) because of its long evolutionary history. The team reconstructed 11 versions of this enzyme from ancient ancestors to the modern bacterium E. coli. They found significant changes in enzyme activity, especially a jump in efficiency at 25 °C. Notably, this increase was not gradual but appeared suddenly during the evolution from one ancestor to another. Researchers discovered that three specific mutations in the enzyme's amino acids greatly improved its activity at lower temperatures. Interestingly, these changes happened far from the enzyme's active site, which challenges earlier beliefs. They also observed a structural shift in the enzyme, which allowed it to work more efficiently at lower temperatures. This shift occurred around 2.5 to 2.1 billion years ago during a time of significant climate change on Earth. The researchers believe that this environmental shift may have influenced how enzymes adapted to cooler temperatures. The findings not only provide insights into how life has adapted over billions of years but could also help in engineering enzymes for use in biotechnology and environmental science. The research shows how organisms have evolved in response to changes in their environments.