Structural basis of substrate progression through the bacterial chaperonin cycle

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• The bacterial chaperonin GroEL-GroES system facilitates protein folding.
• This process involves ATP-regulated cycles of substrate binding, encapsulation, and release.

Purpose of the Study:

• To elucidate the structural dynamics of the GroEL-GroES protein folding mechanism.
• To visualize the conformational changes of the substrate Rubisco during the GroEL-GroES reaction cycle.

Main Methods:

• Cryo-electron microscopy (cryoEM) was employed.
• Structures of GroEL, GroEL-ADP·BeF3, and GroEL-ADP·AlF3-GroES complexed with Rubisco were determined.

Main Results:

• CryoEM structures captured sequential snapshots of Rubisco's conformational changes within the GroEL-GroES cycle.
• Specific charged and hydrophobic GroEL residues mediate initial contacts with non-native Rubisco.
• An asymmetric intermediate GroEL complex was observed upon ATP or ADP·BeF3 binding, with four GroEL subunits binding Rubisco and three in a GroES-accepting conformation.
• Stalled GroEL-ADP·AlF3-Rubisco-GroES complexes revealed Rubisco folding intermediates interacting with GroEL-GroES through diverse residues.

Conclusions:

• The observed asymmetry in the GroEL complex provides insight into GroES recruitment without substrate release.
• The study visualizes the dynamic interactions between GroEL-GroES and its substrate Rubisco throughout the folding process.