Figure 2 – Substrates converted by wild-type NhKHS
chalcone derivative xanthohumol , respectively . Notably , hydration of the prenylated hops chalcone xanthohumol provides access to hydroxyxanthohumol , a natural compound with proven radical scavenging activity in human cancer cell lines . 8 High protein stability in organic solvents , together with optimal temperature and pH , i . e . 35 ° C and pH 5.0 – 6.0 , make NhKHS a promising candidate for the biosynthesis of industrially relevant tertiary alcohols and substrate scope engineering . Moreover , the crystal structure of NhKHS has recently been solved ( PDB ID : 7A0Q ), providing the basis for rational enzyme engineering approaches . Subsequent , as yet unpublished , work at ACIB illustrates the basic structural requirements for NhKHS substrates , as well as the remarkably broad substrate range of this enzyme . Figure 2 shows the substrates converted by wild-type NhKHS ( A ) – kievitone ( 1a ) xanthohumol ( 1b ), 8-prenyl naringenin ( 1c ) and isoxanthohumol ( 1d ) to the respective hydroxylated tertiary alcohol ( 2a-2d ). Structure-based enzyme engineering substantially broadens substrate scope ( B ). Terpenes and their derivatives , collectively termed terpenoids , are a renewable feedstock for the production of high-value and bulk products for diverse industrial sectors . For example , bio-oxidation to monoterpenoids and norisoprenoid natural flavour compounds produced by microbial biotransformation attracts interest in the food , flavour and fragrance industries . ( S )-(+)-linalool is a valuable ingredient for cosmetics , perfumes , household detergents and processed food and beverages , due to its pleasant floral scent . ( R )-(-)-linalool is readily available in essential oils , such as lavender , and can be synthesised both chemically and through biocatalytic routes employing genes and enzymes from lavender . By contrast , ( S )-(+)- linalool is less available through essential oils , because volumes are low . To screen for hydratases that naturally convert terpenoids , or do so upon enzyme engineering is thus highly relevant . Consequently , hydration of β-myrcene has been suggested as a possible route for ( S )-(+)-linalool production ( Figure 3B ). 9 , 10 However , no industrial biotransformation process using linalool desaturase isomerase or other hydratases for ( S )-(+)-linalool production has yet been reported . Back-to-back projects in several groups , including ACIB , have been investigating the 3D structure of CdLDI and its key amino acids involved in ‣
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