Abstract
The GroEL–GroES chaperonin complex is a bacterial protein folding system, functioning in an ATP-dependent manner. Upon ATP binding and hydrolysis, it undergoes multiple stages linked to substrate protein binding, folding and release. Structural methods helped to reveal several conformational states and provide more information about the chaperonin functional cycle. Here, using cryo-EM we resolved two nucleotide-bound structures of the bullet-shaped GroEL–GroES1 complex at 3.4 Å resolution. The main difference between them is the relative orientation of their apical domains. Both structures contain nucleotides in cis and trans GroEL rings; in contrast to previously reported bullet-shaped complexes where nucleotides were only present in the cis ring. Our results suggest that the bound nucleotides correspond to ADP, and that such a state appears at low ATP:ADP ratios.
Highlights
A newly synthesized polypeptide chain should fold in a specific way to form a native structure
Our results indicate that after 20 min of incubation, GroEL–GroES passes through the symmetric cycle
An alternative explanation of the observation is related to the action of the hypothetical substrate: studies carried out in the GH Lorimer laboratory in 2013 showed that symmetric complexes persisted for tens of minutes in the presence of a substrate protein in the reaction mixture, while in its absence football-shaped particles eventually turned into bullet-shaped[34,40]
Summary
A newly synthesized polypeptide chain should fold in a specific way to form a native structure. The term “molecular chaperones”, or “chaperones”, began being applied to large families of proteins that are involved in the folding, ensemble formation, and translocation of macromolecules, but are not involved in the realization of their function. 7 subunits of co-chaperonin GroES with a molecular weight of 10 kDa. each form a dome-shaped complex that is able to bind to the apical domains of GroEL, closing the hydrophobic cavity. Each form a dome-shaped complex that is able to bind to the apical domains of GroEL, closing the hydrophobic cavity This provides rearrangements, which increase the hydrophilicity of the chamber to establish conditions suitable for substrate protein folding[20,21]. It is thought to play an active role: chaperonin functioning requires conformational rearrangements which happen in an ATP-dependent manner and allow for efficient substrate protein binding, folding and release[25]. Recent studies show the importance of the flexible C-terminal regions of GroEL subunits for substrate binding, encapsulation and retention within the c age[26,27,28]
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