Cascade biocatalysis by multienzyme-nanoparticle assemblies.

Multienzyme complexes are of paramount importance in biosynthesis in cells. Yet, how sequential enzymes of cascade catalytic reactions synergize their activities through spatial organization remains elusive. Recent development of site-specific protein-nanoparticle conjugation techniques enables us to construct multienzyme assemblies using nanoparticles as the template. Sequential enzymes in menaquinone biosynthetic pathway were conjugated to CdSe-ZnS quantum dots (QDs, a nanosized particulate material) through metal-affinity driven self-assembly. The assemblies were characterized by electrophoretic methods, the catalytic activities were monitored by reverse-phase chromatography, and the composition of the multienzyme-QD assemblies was optimized through a progressive approach to achieve highly efficient catalytic conversion. Shorter enzyme-enzyme distance was discovered to facilitate intermediate transfer, and a fine control on the stoichiometric ratio of the assembly was found to be critical for the maximal synergy between the enzymes. Multienzyme-QD assemblies thereby provide an effective model to scrutinize the synergy of cascade enzymes in multienzyme complexes.