Mutational Analysis of Linalool Dehydratase-Isomerase (LinD) Suggests Alcohol and Alkene Transformations are Catalyzed Using Non-Covalent Mechanisms

The interconversion of non-activated alkenes and alcohols, catalyzed by (de)hydratases, has great potential in biotechnology for the generation of fine and bulk chemicals. LinD is a cofactor-independent enzyme that catalyzes the reversible (de)hydration of the tertiary alcohol (S)-linalool to the triene beta-myrcene, and also its isomerization to the primary alcohol geraniol. Structure-informed mutagenesis of LinD, followed by activity studies, confirmed essential roles for residues C171, C180 and H129 in water activation for the hydration of beta-myrcene to linalool. However, no evidence of covalent thioterpene intermediates was found using either X-ray crystallography, mass spectrometry, or QM/MM nudged elastic band simula-tions. Labelling and NMR experiments confirmed a role for residue D39 in (de)protonation of the linalool carbon C10 in the isomerization of linalool to geraniol and also the intermediacy of beta-myrcene in this isomerization reaction. X-ray, molecular dynamics and activity studies also suggested a significant role in catalysis for a mobile methionine residue M125, which exists in substantially altered orientations in different mutant structures.