Abstract: Enzymes are capable of accepting a broad range of substrates and are highly selective, manifested as stereoselectivity, positional selectivity, and functional group selectivity. The nature of the enzyme, the predefi ned selective molecular recognition of the substrate molecule within its active site, guides selectivity by discriminating between substrate enantiomers converting only one enantiomer. Enzyme engineering is a powerful tool and a widely accepted methodology to optimize and infl uence enzyme properties, such as the overall activity, selectivity, thermo - and storage stability and the stability toward organic solvents, as it encompasses both directed evolution and rational design. Besides the alteration of enzyme function, enzyme engineering is also capable of directly infl uencing enzyme - catalyzed reactions, thus controlling their product formation. A proof of concept was presented by the divergent evolution of the promiscuous sesquiterpene synthase γ - humulene synthase. The rational design of residues in the active site of the γ - humulene synthase has shown to possess an additive infl uence on protein function and promiscuity. By using this approach, a large number of novel specifi c sesquiterpene synthases has been constructed, each producing one or a few end - products via different reaction pathways including new molecules that do not exist in Nature (Figure 1.1 ) [1] . This instructive example shows the capability to redesign enzyme function by single amino acid substitutions, and to direct the biocatalytic transformation of diverse substrates via the same mechanism. This chapter attempts to demonstrate that dirigent effects have been described infl uencing the outcome of enzyme-catalyzed reactions. It consists of several subchapters that could expand the concept of dirigent properties in biocatalysis by exploiting intrinsic effects which have a considerable impact on the catalytic event of enzyme reactions, but also which extend beyond. First, a brief report is provided of auxiliary or dirigent proteins which play an important role in free - radical coupling in lignin biosynthesis. These naturally evolved proteins capture the oxidized free - radical substrate, providing a scaffold upon which a selective, radical coupling can occur to yield an optically active product. 1
Publication Year: 2013
Publication Date: 2013-01-01
Language: en
Type: article
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