Structure and conformational cycle of a bacteriophage-encoded chaperonin

PLoS One. 2020 Apr 27;15(4):e0230090. doi: 10.1371/journal.pone.0230090. eCollection 2020.


Chaperonins are ubiquitous molecular chaperones found in all domains of life. They form ring-shaped complexes that assist in the folding of substrate proteins in an ATP-dependent reaction cycle. Key to the folding cycle is the transient encapsulation of substrate proteins by the chaperonin. Here we present a structural and functional characterization of the chaperonin gp146 (ɸEL) from the phage EL of Pseudomonas aeruginosa. ɸEL, an evolutionarily distant homolog of bacterial GroEL, is active in ATP hydrolysis and prevents the aggregation of denatured protein in a nucleotide-dependent manner. However, ɸEL failed to refold the encapsulation-dependent model substrate rhodanese and did not interact with E. coli GroES, the lid-shaped co-chaperone of GroEL. ɸEL forms tetradecameric double-ring complexes, which dissociate into single rings in the presence of ATP. Crystal structures of ɸEL (at 3.54 and 4.03 Å) in presence of ATP•BeFx revealed two distinct single-ring conformational states, both with open access to the ring cavity. One state showed uniform ATP-bound subunit conformations (symmetric state), whereas the second combined distinct ATP- and ADP-bound subunit conformations (asymmetric state). Cryo-electron microscopy of apo-ɸEL revealed a double-ring structure composed of rings in the asymmetric state (3.45 Å resolution). We propose that the phage chaperonin undergoes nucleotide-dependent conformational switching between double- and single rings and functions in aggregation prevention without substrate protein encapsulation. Thus, ɸEL may represent an evolutionarily more ancient chaperonin prior to acquisition of the encapsulation mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chaperonin 10 / chemistry
  • Chaperonin 60 / chemistry
  • Chaperonins / chemistry*
  • Cryoelectron Microscopy
  • Escherichia coli / chemistry
  • Escherichia coli Proteins / chemistry
  • Protein Domains
  • Protein Folding*
  • Pseudomonas Phages / chemistry*
  • Pseudomonas Phages / metabolism
  • Pseudomonas aeruginosa / virology*
  • Viral Proteins / chemistry*


  • Chaperonin 10
  • Chaperonin 60
  • Escherichia coli Proteins
  • Viral Proteins
  • Chaperonins

Grants and funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) grant SFB1035 to MH-H and FUH. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.