Introduction of selective intersubunit disulfide bonds into self-assembly protein scaffold to enhance an artificial multienzyme complex's activity.

In nature, many enzymes participating in multienzyme reactions are often assembled to enhance efficiencies of multiple reactions. Therefore, much attention has been focused on self-assembly of multiple enzymes fused with a protein/peptide that interacts with a specific protein to enhance artificial multienzyme reactions. Sulfolobus solfataricus proliferating cell nuclear antigen (PCNA) is a ring-shaped symmetric heterotrimer consisting of PCNA1, PCNA2 and PCNA3. Multiple enzymes can be co-localized on the PCNA ring by fusing them to the C-termini of the three PCNA subunits. However, an advantage of the specific non-covalent complex formation is inextricably associated with the disadvantage of its concentration-dependent dissociation. In this study, disulfide bonds were introduced between the PCNA subunits by Cys substitution at the sites neighboring the interface for heterotrimerization. Selective intersubunit disulfide bond formation between PCNA1 and PCNA3 and between PCNA2 and PCNA3 by a natural oxidizing reagent successfully stabilized an artificial multienzyme complex, which is composed of a bacterial cytochrome P450 and its two redox partner proteins. The covalent stabilization of the multienzyme complex enhanced its cytochrome P450 activity because of the absence of inactive dissociated components.