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Chaperonins are ubiquitously present protein complexes, which assist the proper folding of newly synthesized proteins and prevent aggregation of denatured proteins in an ATP-dependent manner. They are classified into group I (bacterial, mitochondrial, chloroplast chaperonins) and group II (archaeal and eukaryotic cytosolic variants). However, both of these groups do not include recently discovered viral chaperonins. Here, we solved the symmetry-free cryo-EM structures of a single-ring chaperonin encoded by the gene 246 of bacteriophage OBP Pseudomonas fluorescens, in the nucleotide-free, ATPγS-, and ADP-bound states, with resolutions of 4.3 Å, 5.0 Å, and 6 Å, respectively. The structure of OBP chaperonin reveals a unique subunit arrangement, with three pairs of subunits and one unpaired subunit. Each pair combines subunits in two possible conformations, differing in nucleotide-binding affinity. The binding of nucleotides results in the increase of subunits' conformational variability. Due to its unique structural and functional features, OBP chaperonin can represent a new group. Copyright © 2019 Elsevier Inc. All rights reserved.


Tatiana B Stanishneva-Konovalova, Pavel I Semenyuk, Lidia P Kurochkina, Evgeny B Pichkur, Alexander L Vasilyev, Mikhail V Kovalchuk, Mikhail P Kirpichnikov, Olga S Sokolova. Cryo-EM reveals an asymmetry in a novel single-ring viral chaperonin. Journal of structural biology. 2020 Feb 01;209(2):107439

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PMID: 31870903

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