Regulation of a Classical Allosteric Molecular Machine by an Intrinsically Disordered Domain: the C-termini of GroEL

The bacterial chaperonin GroEL, a molecular machine that depends on ATP for its function, undergoes a series of structural changes driven by ATP binding and hydrolysis. These changes power the protein folding reaction within the machine. Researchers have been investigating how the complex allosteric behavior of the GroEL oligomer enables an efficient and directional folding cycle.

A study combining variable-temperature native ion mass spectrometry with single-molecule FRET examined the role of the GroEL C-terminal tails in allostery. They found that these tails restrain the conformational dynamics of the GroEL ring through interactions with the upper apical domains of subunits. As ATP binds, the constraint is gradually lifted, allowing productive engagement by the smaller GroES co-chaperonin.

The study supports the idea that the C-terminal tails function as an entropic regulator of the GroEL reaction cycle, restraining premature ring opening and setting the energetic threshold for productive interactions with GroES. By connecting disordered tail dynamics to the cooperative reorganization of the GroEL ring, this mechanism creates an ordered allosteric cascade that minimizes the formation of empty GroEL-GroES cavities.

The findings suggest that the conformational properties of intrinsically disordered elements can be used to optimize the energetic efficiency and timing of large allosteric machines.