Structural analysis ofSulfolobus solfataricusTF55β chaperonin in open and filamentous states

Chaperonins are biomolecular complexes that assist protein folding. Thermophilic Factor 55 (TF55) is a group II chaperonin found in the archaeal genus Sulfolobus that has α, β and γ subunits. Using cryo-electron microscopy, we have determined the structure of the β-only complex of S. solfataricus TF55 complexes to 3.6–4.2 Å resolution and a filamentous form to 5.2 Å resolution. The structures of the TF55β 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. The structure of the filamentous state indicates how helical protrusions facilitate end-on-end interactions. Synopsis The isolated complex and filamentous forms of TF55β chaperonin from the thermophilic archaea Sulfolobus solfataricus are reported. Using cryo-EM, nucleotide-bound complexes of TF55β at 3.6–4.2 Å resolution reveal an open conformation, while a 5.2 Å reconstruction of the filamentous chaperonin reveals contacts at the apical domain similar to crystal-packed structures.