Residual structure in urea-denatured chaperonin GroEL

Area of Science:

• Biochemistry
• Protein folding
• Molecular chaperones

Background:

• Chaperonins, such as GroEL, are essential molecular machines that assist protein folding.
• Understanding the denaturation and unfolding mechanisms of GroEL is crucial for comprehending protein homeostasis.

Purpose of the Study:

• To investigate the urea-induced denaturation of chaperonin GroEL.
• To characterize the structural changes and identify any residual structures during unfolding.

Main Methods:

• Circular dichroism (CD) spectroscopy to monitor secondary structure changes.
• Intrinsic tyrosine fluorescence to track overall protein conformation.
• Fluorescence spectroscopy using the hydrophobic probe 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonic acid (bisANS) to detect hydrophobic patches.

Main Results:

• GroEL denaturation follows a two-state transition, complete by 3-3.1 M urea, involving oligomer dissociation and monomer unfolding.
• bisANS fluorescence indicates the presence of residual hydrophobic structure in GroEL monomers even after complete unfolding of secondary structure (> 3.1 M urea), as detected by CD.
• This residual structure is not detectable by CD and can be further unfolded by higher urea concentrations.

Conclusions:

• GroEL unfolding is more complex than a simple two-state transition, with residual hydrophobic structures persisting after secondary structure loss.
• The bisANS probe is sensitive to these hydrophobic remnants, providing insights into non-native protein conformations.
• The interaction with bisANS does not significantly alter the overall GroEL structure.