title: Flexible interwoven termini determine the thermal stability of thermosomes.
abstract: Group II chaperonins, which assemble as double-ring complexes, assist in the refolding of nascent peptides or denatured proteins in an ATP-dependent manner. The molecular mechanism of group II chaperonin assembly and thermal stability is yet to be elucidated. Here, we selected the group II chaperonins (cpn-α and cpn-β), also called thermosomes, from Acidianus tengchongensis and investigated their assembly and thermal stability. We found that the binding of ATP or its analogs contributed to the successful assembly of thermosomes and enhanced their thermal stabilities. Cpn-β is more thermally stable than cpn-α, while the thermal stability of the hetero thermosome cpn-αβ is intermediate. Cryo-electron microscopy reconstructions of cpn-α and cpn-β revealed the interwoven densities of their non-conserved flexible N/C-termini around the equatorial planes. The deletion or swapping of their termini and pH-dependent thermal stability assays revealed the key role of the termini electrostatic interactions in the assembly and thermal stability of the thermosomes.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Liu
authors.forename: Kwok-Yan
authors.initials: KY
authors.lastname: Chan
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Pang
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.forename: Zhiyang
authors.initials: Z
authors.lastname: Dong
authors.forename: Fei
authors.initials: F
authors.lastname: Sun
mesh_terms: D041541:Acidianus / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D020285:Cryoelectron Microscopy; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009154:Mutation; D009711:Nucleotides / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D016415:Sequence Alignment; D055672:Static Electricity; D013696:Temperature; D056405:Thermosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D009711:Nucleotides; D000255:Adenosine Triphosphate; D056405:Thermosomes