Herein we report the synthesis and isolation of a shape-persistent Janus protein nanoparticle derived from the biomolecular machine chaperonin GroEL ((A)GroEL(B)) and its application to DNA-mediated ternary supramolecular copolymerization. To synthesize (A)GroEL(B) with two different DNA strands A and B at its opposite apical domains, we utilized the unique biological property of GroEL, i.e., Mg2+/ATP-mediated ring exchange between (A)GroEL(A) and (B)GroEL(B) with their hollow cylindrical double-decker architectures. This exchange event was reported more than 24 years ago but has never been utilized for molecular engineering of GroEL. We leveraged DNA nanotechnology to purely isolate Janus A GroEL B and succeeded in its precision ternary supramolecular copolymerization with two DNA comonomers, A** and B*, that are partially complementary to A and B in (A)GroEL(B), respectively, and programmed to self-dimerize on the other side. Transmission electron microscopy allowed us to confirm the formation of the expected dual-periodic copolymer sequence -((B)*(/B)GroEL(A/A)**(/A)**(/A)GroEL(B/B)*)- in the form of a laterally connected lamellar assembly rather than a single-chain copolymer.