Chaperonin-affected folding of globular proteins

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Folding

Background:

• The chaperone GroEL assists protein folding.
• Understanding GroEL's nucleotide-dependent allosteric control is crucial for protein homeostasis.

Purpose of the Study:

• To investigate the effect of GroEL on the kinetic refolding of alpha-lactalbumin.
• To elucidate the role of nucleotide binding and allosteric regulation in GroEL function.

Main Methods:

• Stopped-flow fluorescence spectroscopy was employed to monitor refolding kinetics.
• Binding constants of GroEL with the folding intermediate were determined at varying nucleotide concentrations (ADP, ATP, ATP analogs).
• GroEL titration with nucleotides (ADP, ATP-γS, AMP-PNP, ATP) was performed.

Main Results:

• ATP binding to GroEL exhibited cooperative behavior, unlike ADP and ATP analogs.
• GroEL binding to the alpha-lactalbumin folding intermediate decreased cooperatively with increasing ATP concentration, but non-cooperatively with ADP.
• A small difference in an allosteric parameter (4.1 for ATP vs. 2.6 for ADP) explains the distinct ATP and ADP-induced transitions.

Conclusions:

• Nucleotide-dependent allosteric control by GroEL governs its interaction with folding intermediates.
• The differential binding and allosteric effects of ATP and ADP are critical for GroEL's chaperone activity.
• These findings provide insights into the molecular mechanisms of protein folding assistance by chaperones.