Recombinant thermosomes from the Acidianus tengchongensis strain S5(T) were purified to homogeneity and assembled in vitro into homo-oligomers (rATcpn alpha or rATcpn beta) and hetero-oligomers (rATcpn alpha beta). The symmetries of these complexes were determined by electron microscopy and image analysis. The rATcpn alpha homo-oligomer was shown to possess 8-fold symmetry while both rATcpn beta and rATcpn alpha beta oligomers adopted 9-fold symmetry. rATcpn alpha beta oligomers were shown to contain the alpha and beta subunits in a 1:2 ratio. All of the complexes prevented the irreversible inactivation of yeast alcohol dehydrogenase at 55 degrees C and completely prevented the formation of aggregates during thermal inactivation of citrate synthase at 45 degrees C. All rATcpn complexes showed trace ATP hydrolysis activity. Furthermore, rATcpn beta 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. (C) 2010 Elsevier Inc. All rights reserved.