GroES in the asymmetric GroEL14-GroES7 complex exchanges via an associative mechanism

Area of Science:

• Molecular biology
• Protein folding mechanisms
• Chaperone-assisted protein processing

Background:

• The chaperonin GroEL, assisted by its cochaperonin GroES, facilitates protein folding within its cavity.
• Understanding the dynamic interaction between GroEL and GroES is crucial for elucidating in vivo protein folding regulation.

Purpose of the Study:

• To investigate the mechanism of GroES exchange on the GroEL chaperonin complex.
• To determine the stoichiometry and stability of GroEL-GroES complexes.
• To elucidate the role of transient complexes in GroES exchange and GroEL cavity accessibility.

Main Methods:

• Electrophoresis in the presence of ADP to separate GroEL and GroES-GroEL complexes.
• Titration experiments using radiolabeled GroES7 with GroEL14.
• Kinetic analysis of GroES and ADP exchange rates.

Main Results:

• A stable 1:1 stoichiometry of GroES7 to GroEL14 was observed, with no stable 2:1 complex detected.
• GroES exchange was demonstrated to be dependent on the concentration of free GroES7, indicating an associative mechanism.
• GroES exchange was significantly faster than ADP exchange, suggesting conformational changes in GroEL14 precede ADP release.

Conclusions:

• GroES exchange occurs through transient, metastable 2:1 complexes, not via free GroEL14 dissociation.
• The dynamic interaction and transient complex formation enable reversible GroEL cavity accessibility for protein substrates under physiological conditions.
• Conformational changes in GroEL14 are essential for ADP release after GroES dissociation, impacting the protein folding cycle.