Enzyme Toolbox

We have a special interest in enzymes with inherited stability. We believe they offer a better starting point to advance the implementation of biocatalysis on large scale. While extremophilic microbes which have adapted to life in  peculiar environments offer an excellent source of biocatalysts, we are also looking at mesophilic organisms which, for less clear reasons, also offer particularly stable enzymes. 

We identify new enzymes by a combination of genomic database scanning and in-silico modelling to handpick possible good hits exploiting our understanding of structural features which induce stability. Mutagenesis is of course also a very powerful tool to increase stability (quaternary structure stabilisation is key) and of course enzyme immobilisation.

Transaminases are a family of enzymes with high potential in biotechnological applications. They can be very useful for the enantioselective production of a series of compounds with high value such as chiral amines and enantiopure amino alcohols which find use in many chemical fields; above all, for the synthesis of biologically active compounds. We have several of these enzymes (both S and R selective) and we have been successfully incorporated them in many flow-based project. 

Acyl-transferases are another very nice class of enzymes which is normally used to make esters. We have developed several projects on an acyl-transferase from Mycobacterium smegmatis which we have used for the scale up of the synthesis of melatonine (an amide) and flavour esters, and we designed a variant which accepts now also thiols for the synthesis of thirsters.  

Redox enzymes encompass a number of different biocatalysts of great industrial interest. We have a collection of enzymes from both salt adapted and mesophilic sources such as alcohol dehydrogenases (ADHs) and ketoreductases (KR) which we have used to synthesise chiral alcohols (in the reductive direction) and in the dynamic kinetic resolution of profenic aldehydes. NADH oxidases (NOXs) can then be combined with these enzymes for the recycling of the cofactor when the primary reaction is the oxidation of alcohols. We have also a nice imine reductase (ImR) which we employed in the synthesis of pipe colic acid.

Amino acid dehydrogenases are also redox enzymes which we use often in combination with other biocatalysts (transaminases for example, but also imine reductases, acyl-transferases etc) and have proven very useful in hydrogen-borrowing systems for the production of valuable chemicals.

Hydrolytic enzymes are another large family of very useful biocatalysts. A selection of esterases and amidases are now part of our library. In a separate project ß-glycosyl hydrolyses, all classified as GH1, have been selected to investigate how environmental adaptation affects biocatalytic properties, as well as stability at different temperatures, pHs and in the presence of solvents. We have looked at this enzymes also in the context of food chemistry applications, such as wine production and hydrolysis of valuable molecules from their glycol-conjugate form.

Cyclases are the latest addition to out lab, in collaboration with Prof. Hauer in Stuttgart we started working with these valuable (and challenging) membrane bound catalysts for the synthesis of precious fragrances.

Semi-synthetic Enzymes and Peptidic Scaffolds

Metals are part of biological molecules and cover different roles. It is fascinating how inorganic elements are pivotal in many cases for biological activity. In collaboration with Prof. Albrecht here in Bern we have started looking at the amino acid residues that hold in place a catalytic metal in the active site of a number of enzymes. Specifically we have investigated the role of histidine as a ligand in copper proteins such as azurin. Azurin is a bacterial blue copper protein that acts as electron shuttle in bacteria denitrification process, where its metal center undergoes oxidation-reduction between Cu(I) and Cu (II) during the electron transfer. We have taken azurin as a model to evaluate the hypothesis that carbon-metal bonding in proteins (other than nitrogen-metal bonding) could play an important role since the interconversion of histidine between the weakly π-acidic imine (N-bound form) and the strongly σ-donating C-bound carbene tautomer is plausible and may have substantial implications on the activity and oxidation-reduction chemistry of the coordinated metal center. We have expanded this research to catalytically active enzyme (NiR) and we are interested in exploring the possible role of carbene incorporation in heme-containing biocatalysts. For recent articles on this topic click here and here.

Peptidic scaffolds. We have in the past worked on natural peptidic scaffolds to incorporate non-natural amino acids for applications in medicinal chemistry . Angiotensin-(1-7) is a heptapeptide hormone of the renin-angiotensin system (RAS) with high potential in anti-cancer therapy for the treatment of patients with unresectable or metastatic sarcomas. By stabilising such structure with a structurally rigid amino acid we labelled ACCA, the activity in vitro of the peptide was significantly enhanced.  However, peptidic scaffolds can be used also to create artificial ligands in metal based catalysis and our research is now exploring the integration of synthetic ligands with enzymes to broaden the in-situ reactivity we can induce.


Flow Biocatalysis

We combine different enzymes, those that offer optimal characteristics for our chemistry, in continuous artificial biocatalytic pathways.

Enzyme Immobilization

Enzyme stability can be greatly enhanced if the biocatalyst is anchored to a support. We develop novel strategies for enzyme immobilization.

Chemo Enzymatic Processes

Flow equipment and compartmenta-lisation of reaction steps offer an exceptional opportunity to integrate enzymes in organic syntheses.