Synthetic modification of a recombinant protein cage called a vault with stimuli-responsive smart polymers provides access to a new class of biohybrid materials; the polymer nanocapsules retain the structure of the protein cage and exhibit the responsive nature of the polymer. Vaults are naturally occurring ubiquitous ribonucleoprotein particles 41 × 41 × 72.5 nm composed of a protein shell enclosing multiple copies of two proteins and multiple copies of one or more small untranslated RNAs. Recombinant vaults are structurally identical but lack the vault content. Poly(N-isopropylacrylamide) (pNIPAAm), a polymer responsive to heat, was conjugated to recombinant vaults that were composed of ~78 copies of the major vault protein (MVP) modified to contain a cysteine rich region at the N-terminus (CP-MVP). The polymer was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization to have a dansyl group at the alpha end and modified to have a thiol-reactive pyridyl disulfide at the omega end, which readily coupled to CP-MVP vaults. The resulting vault nanocapsules underwent reversible aggregation upon heating above the lower critical solution temperature (LCST) of the polymer as determined by electron microscopy (EM), dynamic light scattering experiments, and UV-vis turbidity analysis. The vault structure remained entirely intact throughout the phase transition; suggesting its use in a myriad of biomedical and biotechnology applications.