Structure-based reaction mechanism of oleate hydratase from Elizabethkingia meningoseptica

Hydratases provide access to secondary and tertiary alcohols by regio- and/or stereospecific addition of water to carbon-carbon double bonds. Thereby, hydroxyl groups are selectively introduced without the need for costly co-factor recycling. A number of chemical hydration reactions are impossible currently, for example the regioselective hydration of the cis-9 double bond of oleic acid to yield (R)-10-hydroxy stearic acid, which is the reaction performed by oleate hydratases1. Currently, the applicability of hydratases on an industrial scale is limited primarily by their narrow substrate scope and by restricted information on protein structure and mechanism. Here, the recombinant oleate hydratase originating from Elizabethkingia meningoseptica was biochemically and structurally characterized in the presence of the flavin cofactor. Remarkably, the redox state of FAD does play a role in the bioconversion of oleic acid to (R)-10-hydroxy stearic acid. Deprivation of FAD abolished hydration activity. Reduction of the cofactor to FADH2 enhanced the turnover rate of the reaction by roughly one order of magnitude. Rational amino acid exchange experiments strongly suggest that E122 acts as base and that Y241 concomitantly provides protons in this concerted reaction. Based on the highly conserved regions among oleate hydratases, we are confident that our findings will pave the way for developing this enzyme class for industrial applications in the near future.