Recombinant thermosomes from the Acidianus tengchongensis strain S5^T were purified to homogeneity and assembled in vitro into homo-oligomers (rATcpnα or rATcpnβ) and hetero-oligomers (rATcpnαβ). The symmetries of these complexes were determined by electron microscopy and image analysis. The rATcpnα homo-oligomer was shown to possess 8-fold symmetry while both rATcpnβ and rATcpnαβ oligomers adopted 9-fold symmetry. rATcpnαβ oligomers were shown to contain the α and β subunits in a 1:2 ratio. All of the complexes prevented the irreversible inactivation of yeast alcohol dehydrogenase at 55 °C and completely prevented the formation of aggregates during thermal inactivation of citrate synthase at 45 °C. All rATcpn complexes showed trace ATP hydrolysis activity. Furthermore, rATcpnβ sequestered fully chemically denatured substrates (GFP and thermophilic malic dehydrogenase) in vitro without refolding them in an ATP-dependent manner. This property is similar to previously reported properties of chaperonins from Sulfolobus tokodaii and Sulfolobus acidocaldarius. These features are consistent with the slow growth rates of these species of archaea in their native environment.