Comparison of catalysis by haloalkane dehalogenases in aqueous solutions of deep eutectic and organic solventsElectronic supplementary information (ESI) available. See DOI: 10.1039/c4gc00117f

Haloalkane dehalogenases catalyze the hydrolytic cleavage of carbon-halogen bonds in diverse halogenated hydrocarbons and are attractive catalysts for sustainable biotechnologies. However, their use in industrial processes is limited due to the poor water solubility of their substrates and the tendency of the substrates to undergo abiotic hydrolysis. Here we systematically and critically compare the performance of three haloalkane dehalogenases, DbjA, DhaA and LinB, in aqueous solutions of the deep eutectic solvent ethaline, its components (ethylene glycol and choline chloride), and two organic solvents (methanol and acetone). Each of the solvents had different effects on the activity of each enzyme. Haloalkane dehalogenase DhaA was found to be the most tolerant to ethaline, retaining 21% of its reference activity even in solutions containing 90% (v/v) of ethaline. However, dissolution in 75% (v/v) ethylene glycol, 50% (v/v) methanol, or 25% (v/v) acetone caused almost total loss of DhaA activity. In contrast, the activities of DbjA and LinB were higher in ethylene glycol than in ethaline, and moreover the activity of DbjA was 1.5 times higher in 50% (v/v) ethylene glycol than in pure buffer. Interestingly, the enantioselectivity of 2-bromopentane hydrolysis catalysed by DbjA increased more than 4-fold in the presence of ethaline or ethylene glycol. Our results demonstrate that ethylene glycol and an ethylene glycol-based deep eutectic solvent can have beneficial effects on catalysis by haloalkane dehalogenases, broadening their usability in "green" biotechnologies. Excellent compatibility of ethaline with dehalogenase DhaA was demonstrated by retention of its activity at high ethaline concentration (≥75% v/v).