Nanoscale compartmentalization techniques in cascade catalysis

The highly efficient formation of complex molecules in nature can be attributed to sophisticated, well-developed reaction sequences. In living cells, production of molecules often proceeds via multiple-step cascade reactions. A precise control of the reaction sequence is achieved by positional assembly or spatial allocation of the responsible enzymes. In addition, this strategy suppresses incompatibility issues between the different reactions [1, 2]. Well-known cyclic reaction sequences in nature are the citric acid cycle [3] and the Calvin cycle [4]. Examples of complex linear sequences are fatty acid oxidation [5], the production of vitamin C [6], and taxol synthesis [7], the latter being a highly active natural product that is currently used as a medicine. The transformations are often enantioselective, and the occurrence of undesired side reactions or the formation of waste products is negligible. Transport of labile reaction intermediates occurs sometimes via channels that connect two active sites, called metabolic channeling [8]. Remarkably, the separate enzymatic steps do not hamper each other in an undesired way, and the biocatalysts retain their activity for a prolonged period of time.