All living organisms possess enzymes which are essential for life. Enzymes are proteins able to increase the speed at which chemical reactions happen: they catalyze reactions. Without enzymes we would for instance not be able to digest food fast enough to survive. Enzymes are also very selective for the molecules they act on and very specific for the type of reaction they catalyze. Therefore, in order to perform the wide range of reactions needed for survival, an array of enzymes are needed. Taking the example of food digestion, most mammals, including us humans, do not possess the enzymes needed to fully digest what they eat. Instead we rely on microorganisms, such as bacteria and yeast, living in our digestive tracts to help us.
The enzymes that I studied during my thesis work, called feruloyl esterases, are involved in the degradation of plant material. These enzymes can therefore be found in microorganisms living in digestive tracts, as well as in microorganisms living in soil or growing on trees. Because they can be encountered in very diverse environments and conditions (i.e. pH, temperature) feruloyl esterases with various preferences in term of reaction conditions exist. Because of the reaction they catalyze, feruloyl esterases are of interest to various industries such as bio-refineries, paper mills, or food and feed industries. By modifying the reaction conditions, it is possible to change the reaction direction and make feruloyl esterases link together compounds they otherwise separate. The products of this type of synthetic reaction can be of interest for cosmetic and pharmaceutical industries. In addition, enzyme-based processes are usually conducted at milder temperatures and require less harmful chemicals than the corresponding chemical ones.
Despite the progress made in the past decades, enzymes remain costly to use. In order to decrease the economic impact of using enzymes in industrial processes, several strategies can be used. During my thesis work, I investigated novel esterases, with the aim of finding better ones (e.g. reacting faster, lasting longer). I also looked into the impact of the chosen microorganism for production. In doing so, I observed that some sugar-chain decorations, N‑glycosylation, which some microorganisms add on enzymes during production, are important for the activity and stability of these enzymes. Interestingly, I was able to demonstrate that the length of the sugar-chains changed the preferred reaction temperature of one feruloyl esterase by 10°C.
Another way of reducing the costs of using enzymes is to reuse them. In order to be able to do so we can attach them onto supports, a technique that is called enzyme immobilization. During my project, I used a support that is made of silica and possesses a porous network. The pores of the support allow the immobilization of high amounts of enzyme and can also shelter enzymes. I studied the impact of being immobilized in porous silica support on the activity of some feruloyl esterases. I also used these immobilized feruloyl esterases to evaluate their ability to perform synthetic reactions.
Altogether, these different aspects (picking the right enzyme, producing it efficiently and reusing it after immobilization) will contribute to make the use of enzymes more economically feasible. This will allow for the development of industrial enzyme-based processes that are more respectful of our planet.