Reversible and multi-cyclic protein–protein interaction in bacterial cellulosome-mimic system using rod-shaped viral nanostructure

• The type II cohesin and type II dockerin were cloned from Clostridium thermocellum and expressed in active form with the fusion of TMVcp and EGFP in Escherichia coli.
• We confirmed that the Ca2+-dependent native cohesin-dockerin binding and dissociation between two recombinant fusion proteins, TMVcp-cohesin and EGFP-dockerin.
• The multi-cyclic operation of binding-dissociation between TMVcp-Coh rod and EGFP-dockerin was successfully performed.

The type II cohesin domain and type II dockerin of bacterial cellulosome were cloned from Clostridium thermocellum and expressed with the fusion of tobacco mosaic virus coat protein (TMVcp) and enhanced green fluorescent protein (EGFP), respectively, in Escherichia coli. The TMVcp-cohesin fusion protein was assembled to the stable and rod-shaped nanostructure (TMVcp-Coh rod) under a particular buffer condition, where many active cohesin proteins are biologically and densely displayed around the 3-dimensional surface of TMVcp-Coh rod. Using EGFP-dockerin as a fluorescent reporter, we confirmed that the Ca2+-dependent binding and dissociation between native cohesin and dockerin were reproduced with the two recombinant fusion proteins, TMVcp-cohesin and EGFP-dockerin. The multi-cyclic binding-dissociation operation of TMVcp-Coh rod and EGFP-dockerin was successfully performed with maintaining the reversible cohesin-dockerin interaction in every cycle. EGFP that was fused to dockerin as a proof-of-concept here can be switched to other functional proteins/peptides that need to be used in multi-cyclic operation.