Protein makes medicine greener
The discovery concerns the Gamma Aminobutyric acid (GABA), a substance which works as a neurotransmitter in the brain. Derivatives of GABA work as medicines for epilepsy or affective disorders, for example. The difficulty is that two carbon atoms have to be bonded somewhere along the production process. Joining these two atoms is not only complicated, but also messy. ‘Polluting solvents are used in this process and a large amount of energy is involved. The end product is also not very pure’, says RUG PhD candidate Jan-Ytzen van der Meer, who collaborated with pharmaceutical biology professor Gerrit Poelarends on the project.
It would be nice if there were an enzyme that could handle that task. Enzymes are dissolved in water, function at room temperature and work in a very specific way, but such an environmentally-friendly enzyme does not exist. The researchers came up with a clever plan: Poelarends worked with 4-oxalocrotonate tautomerase, a substance that contains the amino acid Proline. That is a catalyst for the process in which carbon atoms are bound to each other, and the researchers thought that it could have the same effect?
The good news: yes, the enzyme caused the required reaction. However, it was not active enough and also produced the wrong end product: a ‘mirrored’ version, which is unusable for the industry. But Poelarends and Van der Meer did not give up. They went to work on tautomerase so that it would do what they wanted. ‘The good thing is that it is a rather small protein’, explains Van der Meer. ‘It is made up of only 62 amino acids.’
This enabled Van der Meer to make 1,200 ‘mutations’, which he used to look at the effect each had on the efficacy thereafter. ‘From this research a kind of chart emerged. Using this chart, one could see which variants of the enzyme were more active’, he says. He followed the same procedure for the end product: which mutations lead to the right variant being produced? ‘We ultimately merged those two mutations’, says the PhD candidate. ‘The end result is an enzyme in which two positions have been given a different amino acid.’
‘It is the first time that an enzyme has been analysed so systematically’, says Van der Meer. The enzyme which has been produced is only suitable for the creation of GABA variants, but the method will be imitated, he suspects. ‘This was a small enzyme, but for the larger enzymes, research is certainly heading in that direction.’