The glow points the way: coupled enzyme test helps in the search for the right biocatalyst

The chemical industry is going biological: the use of biocatalysts, called enzymes, allows many products to be prepared very efficiently, economically, and in an environmentally safe manner.

For a specific reaction, however, finding the right enzyme among the countless natural enzymes is like finding a needle in a haystack. British researchers have now developed a screening method that could allow such a search to be tackled systematically, relatively rapidly, and simply.

Most reactions that chemists would like to carry out in their reactors do not occur in nature. It is thus understandable that nature does not as a rule simply have a suitable enzyme available. However, sometimes one can be found that, in addition to its intended task, will also catalyze the desired reaction – even if with only low activity. Many enzymes also convert compounds that resemble their natural substrate (substrate ambiguity), while others even catalyze different types of reactions (catalyst promiscuity). An enzyme that demonstrates a certain activity for the desired reaction can often be sufficiently optimized by targeted mutations to become useful for production.

But how to find such an enzyme? John D. Sutherland and his team at the University of Manchester have used a sample reaction, the conversion of an alcohol into an aldehyde, to demonstrate how this might work. The secret of their success is the coupling of the desired reaction to a second reaction that can be easily detected. This is how it goes: The researchers fragment the complete DNA of a microorganism and incorporate the individual fragments into bacteria. These form colonies that produce many copies of the corresponding proteins. All of the colonies together represent all of the proteins of the microorganism, its proteome. The alcohol to be converted is then added to the medium. If one of the colonies contains a useful enzyme, the alcohol is converted into an aldehyde. The trick is this: An additional gene that codes for the enzyme luciferase was implanted into all of the bacteria. Luciferase converts aldehydes into their corresponding acids. This process releases energy in the form of light. Colonies in which the alcohol is converted into the desired aldehyde can easily be recognized by their glow. The detection is so sensitive that even very low enzymatic activities are obvious. Glowing colonies are then selected and the sought-after, alcohol-converting enzyme is identified by means of the foreign gene fragment.