Structural analysis of the Sulfolobus solfataricus TF55β chaperonin by cryo-electron microscopy

Chaperonins are biomolecular complexes that assist in protein folding. Thermophilic factor 55 (TF55) is a group II chaperonin found in the archaeal genus Sulfolobus that has alpha, beta and gamma subunits. Using cryo-electron microscopy, structures of the beta-only complex of S. solfataricus TF55 (TF55beta) were determined to 3.6-4.2 A resolution. The structures of the TF55beta complexes formed in the presence of ADP or ATP highlighted an open state in which nucleotide exchange can occur before progressing in the refolding cycle.