Inhibitory Effect of DMSO on Halohydrin Dehalogenase: Experimental and Computational Insights into the Influence of an Organic Co?solvent on the Structural and Catalytic Properties of a Biocatalyst
Pros and cons considered: Halohydrin dehalogenases (HHDHs) are versatile enzymes employed in the synthesis of chiral building blocks. To increase substrate solubility, DMSO stands out as the most commonly used co?solvent. Here we found that DMSO acts as an inhibitor of the enzyme HheC. To understand the observed phenomena at the molecular level, in?depth experimental studies were performed in combination with molecular dynamics simulations.Although the application of organic solvents in biocatalysis is well explored, in?depth understanding of the interactions of solvent with proteins, in particular oligomeric ones, is still scant. Understanding these interactions is essential in tailoring enzymes for industrially relevant catalysis in nonaqueous media. In our study, the homotetrameric enzyme halohydrin dehalogenase (HHDH) from Agrobacterium radiobacter AD1 (HheC) was investigated, as a model system, in DMSO/water solvent mixtures. DMSO, the most commonly used co?solvent for biocatalytic transformations, was found to act as a mixed?type inhibitor with a prevalent competitive contribution. Even 5?% (v/v) DMSO inhibits the activity of HheC by half. Molecular dynamics (MD) simulations showed that DMSO keeps close to Ser?Tyr catalytic residues forming alternate H?bonds with them. Stability measurements paired with differential scanning calorimetry, dynamic light scattering methods and MD studies revealed that HheC maintains its structural integrity with as much as 30?% (v/v) DMSO.