ATP-bound states of GroEL captured by cryo-electron microscopy

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Machines

Background:

• The chaperonin GroEL facilitates protein folding through a cyclical process involving ATP binding and hydrolysis.
• GroEL functions as a double-ring complex, with each ring capable of binding ATP and substrate.
• Understanding the mechanism of GroEL's cooperative function is key to comprehending protein homeostasis.

Purpose of the Study:

• To elucidate the structural basis of the chaperonin GroEL's protein-folding cycle.
• To investigate the role of ATP binding in GroEL's conformational changes and cooperativity.
• To develop structural models explaining ATP-induced substrate release and inter-ring cooperativity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of GroEL-ATP complex.
• Atomic structure fitting into cryo-EM density maps.
• Analysis of structural changes upon ATP binding to GroEL and GroEL-GroES-ADP complexes.

Main Results:

• The GroEL-ATP structure reveals downward rotation of intermediate domains.
• Switching of intersubunit salt bridge contacts from substrate to ATP binding domains was observed.
• Structural data suggest models for reduced polypeptide affinity and cooperativity upon ATP binding.

Conclusions:

• The study provides a structural mechanism for ATP-induced conformational changes in GroEL.
• A model for cooperativity in GroEL, involving salt bridge switching, is proposed.
• These findings offer insights into cooperativity in other ring-shaped molecular machines.