Thesis Subject:
Linalool Dehydratase-Isomerase and Linalool-Isomerase

Scientific Interests and Goals:
The volatile organic compounds represent over 1 % of the primary production by plants. The atmosphere receives annually an import of 1180 Teragram VOC per year, including 480 Teragram monoterpenes (C10H16), which are natural hydrocarbons. The immission of VOC from plants into the soil is not known, but large populations of monoterpene-utilizing bacteria suggest a significant transfer rate. Monoterpenes are constituents of essential oils and serve as precursors for biological compounds. Local climate can also be influenced by the emission of high amounts of monoterpenes, e.g. in coniferous forests. Monoterpenes and derivatives have been investigated regarding their aseptic properties, their medical potential in cancer research and pharmacological application area.
The microbial degradation of monoterpenes and their oxygenated derivatives under aerobic conditions is well studied and the intital activation reactions are catalyzed by oxygenases. In the absence of molecular oxygen alternative enzyme are needed. The Betaproteobacteria Castellaniella defragrans 65Phen and Thauera linaloolentis 47Lol are able to use monoterpenes as sole carbon and energy source under denitrifying conditions. Myrcene, a pure hydrocarbon, is activated by introduction of a hydroxyl group by the novel enzyme linalool dehydratase-isomerase (LDI) from C. defragrans 65Phen. The enzyme hydratizes myrcene stereoselective into (S)-(+)-linalool and further isomerizes (S)-(+)-linalool into geraniol. The enzyme has already been purified and successfully expressed in E. coli. In its active form it is a homotetramer and it shows high sensitivity towards molecular oxygen, but is not irreversibly inhibited. Due to the bifunctionality and the novel enzymatic functions of the LDI it has been placed as the first member of a new enzyme family and two EC numbers have been assigned, 4.2.1.127 for the dehydratase and 5.4.4.4 for the isomerase. So far, nothing is known about the structure and the enzymatic mechanism of the LDI on the molecular level. In this project the structure will be elucidated by X-ray crystallography and the enzymatic mechanism will be studied.

A linalool isomerase (LI) activity has been detected in the Betaproteobacterium Thauera linaloolentis 47Lol. This organism has been isolated on the monoterpene alcohol linalool. Investigations showed the formation of geraniol with linalool as substrate. The LDI as well as the LI catalyse an isomerization of the tertiary alcohol linalool into the primary alcohol geraniol, a rather uncommon reaction in nature. In most cases, tertiary alcohols are considered to be dead-end products.
So far, the enzyme has not been purified or characterized. In this project, an already initiated purification protocol for the enzyme will be optimized. The LI will be characterized with respect to its kinetics and conditions optimal for its activity. Further, it will be investigated if there is a relationship between the two enzymes, as they catalyze the same reaction.

Selected Publications:
Brodkorb D., Gottschall M., Marmulla R., Lüddeke F., Harder J. Linalool dehydratase-isomerase, a bifunctional enzyme in the anaerobic degradation of monoterpenes. (2010) Journal of Biological Chemistry 285:30436-30442

Siebert H.-M., Marmulla R., Stahmann K.-P. Effect of SDS on planctonic Acidithiobacillus thiooxidans and bioleaching of sand samples. (2011) Minerals Engineering 24:1128-1131