Heterogeneous Systems Biocatalysis: The Path to the Fabrication of Self-Sufficient Artificial Metabolic Cells

Industrial biocatalysis is playing a key role in the development of the global bio-economy that must change our current productive model to pair the socio-economical development with the preservation of our already harmed planet. The exploitation of isolated multi-enzyme systems and the discovery of novel biocatalytic activities are leading us to manufacture chemicals that were inaccessible through biological routes in the early past. These endeavors have been grouped under the concept of systems biocatalysis. However, by using isolated biological machineries, fundamental features underlying the protein confinement found inside the living cells are missed. To re-gain these properties, such concepts can be expanded to a new concept; heterogeneous systems biocatalysis. This new concept is based on the fabrication of heterogeneous biocatalysts inspired by the spatial organization and compartmentalization that orchestrate metabolic pathways within cells. By assembling biological machineries (including enzymes and cofactors) into artificial solid chassis, one can fabricate self-sufficient and robust cell-free systems able to catalyze orchestrated chemical processes. Furthermore, the confinement of enzymes and and "artificial cofactor" inside solid materials has also attracted our attention because these self-sufficient systems exert de novo and non-natural functionalities. Here, we intend to go beyond immobilization of multi-enzyme systems, discussing only those enzymatic systems that have been co-immobilized with their cofactor or exogenous partners to enhance their cooperative action. In this article, we review the latest architectures developed to fabricate self-sufficient heterogeneous biocatalysts with application in chemical manufacturing, biosensing or energy production.