Epoxide hydrolases catalyze the hydrolysis of epoxides to corresponding diols, which is important in detoxification, synthesis of signal molecules, or metabolism. Limonene-1,2- epoxide hydrolase (LEH) differs from many other epoxide hydrolases in its structure and its novel one-step catalytic mechanism. Its main fold consists of a six-stranded mixed beta-sheet, with three N-terminal alpha helices packed to one side to create a pocket that extends into the protein core. A fourth helix lies in such a way that it acts as a rim to this pocket. Although mainly lined by hydrophobic residues, this pocket features a cluster of polar groups that lie at its deepest point and constitute the enzyme's active site.