Recyclable cellulose-containing magnetic nanoparticles: immobilization of cellulose-binding module-tagged proteins and a synthetic metabolon featuring substrate channeling.

Easily recyclable cellulose-containing magnetic nanoparticles were developed for immobilizing family 3 cellulose-binding module (CBM)-tagged enzymes/proteins and a self-assembled three-enzyme complex called the synthetic metabolon. Avicel (microcrystalline cellulose)-containing magnetic nanoparticles (A-MNPs) and two controls of dextran-containing magnetic nanoparticles (D-MNPs) and magnetic nanoparticles (MNPs) were prepared by a solvothermal method. Their adsorption ability was investigated by using CBM-tagged green fluorescence protein and phosphoglucose isomerase. A-MNPs had higher adsorption capacity and tighter binding on CBM-tagged proteins than the two control MNPs because of the high-affinity adsorption of CBM on cellulose. In addition, A-MNPs were used to purify and co-immobilize a three-enzyme metabolon through a CBM-tagged scaffoldin containing three different cohesins. The three-enzyme metabolon comprised of dockerin-containing triosephosphate isomerase, aldolase, and fructose 1,6-bisphosphatase was self-assembled because of the high-affinity interaction between cohesins and dockerins. Thanks to spatial organization of the three-enzyme metabolon on the surface of A-MNPs, the metabolon exhibited a 4.6 times higher initial reaction rate than the non-complexed three-enzyme mixture at the same enzyme loading. These results suggested that the cellulose-containing MNPs were new supports for immobilizing enzymes, which could be selectively recycled or removed from other biocatalysts by a magnetic force, and the use of enzymes immobilized on A-MNPs could be very useful to control the On/Off process in enzymatic cascade reactions.