engleski

Elucidation of DMSO effects on catalytic activity of halohydrin dehalogenase HheC by molecular dynamics

Homotetrameric halohydrin dehalogenase from Agrobacterium radiobacter AD1, HheC is extensively used for industrial green synthesis of enantiopure building blocks. It naturally catalyses reversible dehalogenation of vicinal haloalcohols, but it is utilized with a whole range of unnatural nucleophiles in epoxide ring-opening reactions. In order to increase solubility of lipophilic epoxides and conversion efficiency, addition of various solvent is explored. The results of our study of effects of widely explored solvent DMSO (dimethyl sulfoxide) on catalytic activity of HheC will be presented. Besides determination of kinetic parameters, differential scanning calorimetry (DSC) and dynamic light scattering (DLS), molecular dynamics (MD) is used to elucidate mechanisms of DMSO action on HheC. We carried out MD simulations (GROMACS) on natural tetrameric and hypothetical monomeric HheC in water as well as in 20% and 50% (v/v) DMSO/aqueous environment. The tetramer HheC exhibits remarkable conformational tolerance towards DMSO up to 30% and it instantly aggregates at 50% DMSO, but its catalytic activity exponentially decreases with DMSO addition. 5% DMSO inhibits the HheC activity by half. The MD demonstrates that while subunit conformations slightly changes with DMSO addition, distinct sheering of the main structural motifs between subunits occurs, with changes proceeding from more localized (20%) to more extended and collective (50%). However, no dissociation (up to 300 ns) was observed in accordance with DSC and DLS results, but buried surface area increases and the catalytic site becomes more constrained. DMSO is found to replace H2O molecules in the catalytic site forming alternately H-bonds with the catalytic amino acid residues S132 and Y145, and to form small clusters around the protein (Fig. 1).

halohydrin dehalogenase ; biocatalysis: dimethyl sulphoxide ; molecular dynamics: DLS ; DSC

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