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Interaction of GroEL with a highly structured folding intermediate: iterative binding cycles do not involve unfolding
1Institut für Biophysik und Physikalische Biochemie, Universität Regensburg, Germany.
Summary
Molecular chaperones GroEL bind nonnative proteins based on general surface properties, not specific folding stages. ATP binding to GroEL appears to inhibit reassociation, not promote substrate release during protein folding.
Area of Science:
- Molecular biology
- Protein biophysics
Background:
- GroE proteins, including GroEL, are molecular chaperones essential for protein folding.
- The precise mechanism of GroEL-mediated folding and the state of bound nonnative proteins remain unclear.
- It is debated whether GroEL binds proteins at specific folding stages and if binding induces unfolding.
Purpose of the Study:
- To investigate the binding properties of GroEL using folding intermediates of an antibody fragment.
- To determine the folding stage requirements for GroEL binding.
- To clarify whether GroEL binding causes unfolding of nonnative proteins.
Main Methods:
- Utilized folding intermediates of an Fab antibody fragment as molecular probes.
- Defined GroEL binding properties by analyzing interactions with different folding states.
- Quantitatively analyzed reactivation kinetics in the presence and absence of ATP.
Main Results:
- GroEL binds to both early and late quaternary-structured folding intermediates (Dc).
- Binding to GroEL does not necessarily cause unfolding of highly structured intermediates.
- ATP binding to GroEL appears to inhibit reassociation of the substrate, rather than promoting release.
Conclusions:
- GroEL binding is dictated by general surface properties of nonnative proteins, not a specific folding stage.
- Unfolding is not an obligatory consequence of GroEL binding to structured intermediates.
- ATP's role in the GroEL-mediated folding cycle involves inhibiting reassociation.