Engineering substrate channeling in biosystems for improved efficiency

The efficiency of a biochemical reaction is contextually regulated in the landscape of the metabolic network of a cell. The availability and activity of the corresponding enzyme are maintained at a level that favors the overall fitness of the cell, constituting a big issue for biotechnology application that a substantial accumulation of specific product is principally expected. Substrate channeling mechanism naturally existing in multiple active site enzymes, enhances the catalytic efficiency of the involved enzymes via the proximity effect enabled by the'evolutionally optimized'orientation of the enzymes. In metabolic engineering or in vitro cascade biocatalysis, improved efficiency can be obtained when the involved enzymes are rationally organized, to simulate substrate channeling mechanism in artificially constructed systems. In this paper, we reviewed the available approaches adopted in constructing in vitro cascade biocatalysis or in vivo engineered pathways for the production of valuable products. Among these approaches, assembling enzymes onto the designed scaffolds (protein, DNA or RNA) has been proved effective in many metabolic engineering studies. Encapsulating enzymes in virus capsid or encapsulin can be used to create specialized 'organelle-like' microreactors in cell by simulating the naturally existing bacterial microcompartment. Assembling enzymes on lipid droplet or thylakoid membrane of chloroplasts, will be of particular significance in practice in plant cell bioreactors. Inclusion of a feedback mechanism as an addition to these engineered systems may promise further increased efficiency. (c) 2018 Society of Chemical Industry