Thermosome: A Group II Chaperonin of Archaea

Abstract

Chaperonin, heat shock protein 60, plays an important role in the proteostasis of cytosol. Chaperonins are divided into two groups: group I and group II. Group II chaperonins exist in eukaryotes and archaea, and these chaperonins are named CCT/TRiC and Thermosome, respectively. Group II chaperonins have almost the same structure as group I chaperonins. The main difference is the existence of a helical protrusion, which constitutes a built-in lid of the cavity. Group II chaperonin captures an unfolded protein in the cavity in the open conformation and changes to the closed conformation in an ATP-dependent manner, which triggers folding of the captured protein. As Thermosome is relatively stable and simple compared with CCT, the conformational change mechanism and also the interaction with co-chaperone, Prefoldin, have been studied in detail using Thermosome. The conformational change procedure of Thermosome will give insights on protein folding mechanism by group II chaperonins.

Key Concepts

• Group II chaperonin is an essential cytosolic molecular chaperone in eukaryotes and archaea.
• The archaeal group II chaperonin is named Thermosome.
• Group II chaperonin has a built-in lid for the central cavity.
• As ATP induces a conformational change from the open to the closed conformation, twisting of the ring occurs.
• Group II chaperonin cooperates with a co-chaperone, Prefoldin, which captures an unfolded protein and transfers it to the central cavity of the group II chaperonin.