Synthetic enzyme supercomplexes: co-immobilization of enzyme cascades

Abstract

A sustainable alternative to traditional chemical synthesis is the use of enzymes as biocatalysts. Using enzymes, different advantages such as mild reaction conditions and high turnover rates are combined. However, the approach of using soluble enzymes suffers from the fact that enzymes have to be separated from the product post-synthesis and can be inactivated by this process. Therefore, enzymes are often immobilized to solid carriers to enable easy separation from the product as well as stabilization of the enzyme structure. In order to mimic the metabolic pathways of living cells and thus to create more complex bioproducts in a cell-free manner, a series of consecutive reactions can be realized by applying whole enzyme cascades. As enzymes from different host organisms can be combined, this offers enormous opportunities for creating advanced metabolic pathways that do not occur in nature. When immobilizing this enzyme cascades in a co-localized pattern a further advantage emerges: as the product of the previous enzyme is directly transferred to its co-immobilized subsequent catalyst, the overall performance of the cascade can be enhanced. Furthermore when enzymes are in close proximity to each other, the generation of by-products is reduced and obstructive effects like product inhibition and unfavorable kinetics can be disabled. This review gives an overview of the current state of the art in the application of enzyme cascades in immobilized forms. Furthermore it focuses on different immobilization techniques for structured immobilizates and the use of enzyme cascade in specially designed (microfluidic) reactor devices.