(Invited) Chimeric and Single-Site Mutant Enzymes for the Design of Nanostructured Bioelectrodes in Enzymatic Fuel Cells and Sensors

摘要

Control over redox enzyme immobilization and electrical interfacing at electrode is a major challenge when building an electrode for enzymatic sensor or fuel cell. An adequate environment has to be created in order to maximize the number of active enzymes and minimize electron transfer distances between enzyme active sites and conductive surfaces or redox partners. In this respect, the production of specific mutants is a powerful way to introduce a level of control over orientation and organization of redox enzymes at the electrode. In addition, the combination of these enzymes with nanomaterials is aimed at maximizing the number of wired enzymes per surface unit while also providing rapid electron transfer pathways and enhancing electrocatalytic current densities. A chimeric protein can be designed by combining a prion domain and a small iron-sulfur redox protein such as rubredoxin. Thanks to the ability of the prion domain to self-assemble in amyloid fibers, protein-only redox nanowires can be produced. These protein nanowires are able to entrap redox enzymes such as multicopper enzymes or [NiFe] hydrogenases, while ensuring interprotein electron transport between enzyme active sites and electrode surface. Chimeric laccases was also designed by combining this multicopper enzyme with a hydrophobin domain. In this case, hydrophobin strongly interacts with the pi-extended network of chemically-exfoliated graphene or carbon nanotubes. These biofunctionalized nanomaterials were used in electrochemical sensors for polyaromatic and phenolic compounds. Single-site mutation at the surface of enzymes is also a powerful means to control the immobilization and orientation of enzymes at the surface of nanostructured electrodes. We have especially investigated the covalent and non-covalent functionalization of single-site mutant laccases for the rational immobilization and direct wiring of the enzymes at the surface of carbon nanotubes and gold nanoparticles. These nanomaterials are able to provide novel self-assembled nanostructured redox bioassembly or favor heterogeneous electron transfer to the enzyme by promoting specific orientations.