NOVELTY - Nanoparticle-chaperonin (GroEL) protein complex comprises: (a) first GroEL subunit variant comprising: (i) fully defined 548 amino acids (SEQ ID NO. 1) given in the specification; and (ii) one or more amino acid residues other than the alanine residue of No. 52 and No. 398 substituted in SEQ ID NO. 1; and (b) second GroEL subunit variant comprising an amino acid sequence having deletion or addition mutation and having molecular chaperone activity. The nanoparticle comprises ring-shaped nanoparticle structure that is included in the space surrounded by GroEL subunits of the GroEL variants.    USE - The nanoparticle-GroEL protein complex is useful in electrode material (for photoelectric conversion, reaction catalyst, fuel cell, and secondary battery), catalyst material, photoelectric chemical energy conversion system, photoelectric chemical hydrolyzing system, and photoresponsive function materials (e.g. photoelectric conversion element material, optical collection antenna, and optical response nano-sensing element).    ADVANTAGE - The nanoparticle-GroEL protein complex has stable ring-shaped nanoparticle structure.    DETAILED DESCRIPTION - Nanoparticle-chaperonin (GroEL) protein complex comprises: (a) first GroEL subunit variant comprising: (i) fully defined 548 amino acids (SEQ ID NO. 1) given in the specification; and (ii) one or more amino acid residues other than the alanine residue of No. 52 and No. 398 substituted in SEQ ID NO. 1; and (b) second GroEL subunit variant comprising an amino acid sequence having deletion or addition mutation and having molecular chaperone activity. The nanoparticle comprises ring-shaped nanoparticle structure that is included in the space surrounded by GroEL subunits of the GroEL variants. It has less than or equal to 2 nm in diameter. The complex has a ring-shaped nanoparticle structure arranged in the state in which the nanoparticles are spaced apart in the region of 4-10 nm in diameter. An INDEPENDENT CLAIM is a method for preparing nanoparticle-GroEL protein complex comprising contacting ring-shaped nanoparticle structure and GroEL subunits of the GroEL variants in the state in which the nanoparticles are spaced apart, where the GroEL subunit variants comprise first GroEL subunit variant comprising SEQ ID NO. 1 and one or more amino acid residues other than the alanine residue of No. 52 and No. 398 substituted in SEQ ID NO. 1; and second GroEL subunit variant comprising an amino acid sequence having deletion or addition mutation and having molecular chaperone activity.