Characterization of an epoxide hydrolase from the Florida red tide dinoflagellate, Karenia brevis

Epoxide hydrolases are believed to be key enzymes in the biosynthesis of brevetoxins. Significant differences in epoxide hydrolase activity and expression in high and low toxin strains of Karenia brevis support this hypothesis. [Display omitted] •An epoxide hydrolase (EH) from Karenia brevis is cloned and expressed.•Substrate selectivity of expressed EH is characterized.•High toxic Karenia brevis has higher EH activity when compared to a low toxic strain. Epoxide hydrolases (EH, EC 3.3.2.3) have been proposed to be key enzymes in the biosynthesis of polyether (PE) ladder compounds such as the brevetoxins which are produced by the dinoflagellate Karenia brevis. These enzymes have the potential to catalyze kinetically disfavored endo-tet cyclization reactions. Data mining of K. brevis transcriptome libraries revealed two classes of epoxide hydrolases: microsomal and leukotriene A4 (LTA4) hydrolases. A microsomal EH was cloned and expressed for characterization. The enzyme is a monomeric protein with molecular weight 44kDa. Kinetic parameters were evaluated using a variety of epoxide substrates to assess substrate selectivity and enantioselectivity, as well as its potential to catalyze the critical endo-tet cyclization of epoxy alcohols. Monitoring of EH activity in high and low toxin producing cultures of K. brevis over a three week period showed consistently higher activity in the high toxin producing culture implicating the involvement of one or more EH in brevetoxin biosynthesis.