Multienzyme complexes, or metabolons, are assemblies or clusters of sequential enzymes that naturally exist in metabolic pathways. These nanomachineries catalyze the conversion of metabolites more effectively than the freely floating enzymes by minimizing the diffusion of intermediates in vivo. Bioengineers have devised synthetic versions of multienzyme complexes in cells to synergize heterologous biosynthesis, to improve intracellular metabolic flux, and to achieve higher titer of valuable chemical products. Here, we utilized orthogonal protein reactions (SpyCatcher/SpyTag and SnoopCatcher/SnoopTag pairs) to covalently assemble three key enzymes in the mevalonate biosynthesis pathway and showed 5-fold increase of lycopene and 2-fold increase of astaxanthin production in Escherichia coli. The multienzyme complexes are ellipsoidal nanostructures with hollow interior space and uniform thickness and shapes. Intracellular covalent enzyme assembly has yielded catalytic nanomachineries that drastically enlarged the flux of carotenoid biosynthesis in vivo. These studies also deepened our understanding on the complexity of hierarchical enzyme assembly in vivo.
Keywords: SpyCatcher and SpyTag; biosynthesis; carotenoids; covalent assembly; multienzyme complex.