Increasing the Catalytic Performance of a Whole Cell Biocatalyst Harboring a Cytochrome P450cam System by Stabilization of an Electron Transfer Component

Chemoenzymatic Synthesis of a Novel Borneol-Based Polyester

Terpenes are a class of natural compounds that have recently moved into the focus as a bio-based resource for chemical production, owing to their abundance, their mostly cyclic structures, and the presence of olefin or single hydroxy groups. To apply this raw material in new industrial fields, a second hydroxy group is inserted into borneol by cytochrome P450cam (CYP101) enzymes in a whole-cell catalytic biotransformation with Pseudomonas putida KT2440. Next, a semi-continuous batch system was developed to produce 5-exo-hydroxyborneol with a final concentration of 0.54 g L^-1 . The bifunctional terpene was then used for the synthesis of a bio-based polyester by a solvent-free polycondensation reaction. The resulting polymer showed a glass transition temperature of around 70 °C and a molecular weight in the range of 2000-4000 g mol^-1 (M_w ). These results show that whole-cell catalytic biotransformation of terpenes could lead to bio-based, higher-functionalized monomers, which might be basic raw materials for different fields of application, such as biopolymers.

Terpene hydroxylation with microbial cytochrome P450 monooxygenases

Terpenoids comprise a highly diverse group of natural products. In addition to their basic carbon skeleton, they differ from one another in their functional groups. Functional groups attached to the carbon skeleton are the basis of the terpenoids' diverse properties. Further modifications of terpene olefins include the introduction of acyl-, aryl-, or sugar moieties and usually start with oxidations catalyzed by cytochrome P450 monooxygenases (P450s, CYPs). P450s are ubiquitously distributed throughout nature, involved in essential biological pathways such as terpenoid biosynthesis as well as the tailoring of terpenoids and other natural products. Their ability to introduce oxygen into nonactivated C-H bonds is unique and makes P450s very attractive for applications in biotechnology. Especially in the field of terpene oxidation, biotransformation methods emerge as an attractive alternative to classical chemical synthesis. For this reason, microbial P450s depict a highly interesting target for protein engineering approaches in order to increase selectivity and activity, respectively. Microbial P450s have been described to convert industrial and pharmaceutically interesting terpenoids such as ionones, limone, valencene, resin acids, and triterpenes (including steroids) as well as vitamin D3. Highly selective and active mutants have been evolved by applying classical site-directed mutagenesis as well as directed evolution of proteins. As P450s usually depend on electron transfer proteins, mutagenesis has also been applied to improve the interactions between P450s and their respective redox partners. This chapter provides an overview of terpenoid hydroxylation reactions catalyzed by bacterial P450s and highlights the achievements made by protein engineering to establish productive hydroxylation processes.