An ultra-stable artificial protein cage was created by using TRAP (trp RNA-binding attenuation protein). Adding a gold (I) triphenylphosphine compound to a cysteine-substituted TRAP generated a cage 22 nm in diameter. The TRAP cage resisted severe conditions, such as high temperature, denaturing agents, and acidic and basic solvents. However, it was instantly disassembled when reducing agents were added to the solution. We can therefore fully control both assembly and disassembly of the TRAP cage. Cryo-EM single-particle analysis revealed a chiral pair of TRAP cages and their atomic structures, in which gold atoms acted as staples to connect the TRAP rings.