Mechanism of Action of Group II Chaperonins:

Chaperonins are highly allosteric double-ring ATPases that mediate
cellular protein folding. ATP binding and hydrolysis control
opening and closing of the central chaperonin chamber which
transiently provides a protected environment for protein folding.
During evolution, two distinct strategies to close the chaperonin
chamber have emerged. Archaeal and eukaryotic chaperonins contain a
built-in lid, whereas bacterial chaperonins use a ring-shaped
cofactor as a detachable lid. The present work contributes to the
current mechanistical understanding of group II chaperonins by
unraveling key functions of the built-in lid. In addition to
physically encapsulating the substrate, the lid-forming apical
protrusions also play a key role in regulating chaperonin function
and ensuring its activity as a “two-stroke” molecular machine. By
comparative investigation of two distinct chaperonin systems,
namely TRiC and Mm-Cpn, this study uncovers a remarkable degree of
mechanistic and functional conservation between group II
chaperonins from eukaryotic and archaeal origin, despite their
evolutionary distance.