Multi-enzyme systems: bringing enzymes together in vitro

In living cells enzymes catalyze a wide variety of metabolic processes, which involve multiple reaction steps. Efficient transfer of the intermediates from one catalytic site to the other is achieved by the formation of macromolecular enzyme complexes. This phenomenon, called metabolic channeling, has inspired researchers to bring biocatalysts together in an artificial way as well. This review describes the various in vitro strategies which have been exploited so far. A distinction is made based on the degree of control over the assembly process. Non-specific, covalent co-immobilization as well as non-covalent encapsulation, scaffold-mediated co-localization and site-specific covalent conjugation strategies are discussed.