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GroEL stability and function. Contribution of the ionic interactions at the inter-ring contact sites
Begoña Sot1, Sonia Bañuelos, Jose María Valpuesta
1Unidad de Biofísica, Consejo Superior de Investigaciones Científicas-Universidad del País Vasco Euskal Herriko Unibertsitatea and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48080 Bilbao, Spain.
The Journal of Biological Chemistry
|June 11, 2003
Summary
Ionic interactions in the chaperonin GroEL are crucial for protein folding regulation and maintaining cellular temperature homeostasis. These interactions control substrate binding and ensure proper function at physiological temperatures.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Dynamics
Background:
- Chaperonin GroEL facilitates protein folding via allosteric communication between its double ring structure.
- ATP binding induces simultaneous positive intra-ring and negative inter-ring cooperativities, crucial for the protein folding cycle.
- Understanding inter-ring allosterism is key to elucidating GroEL's regulatory mechanisms.
Purpose of the Study:
- To investigate the role of inter-ring ionic interactions in GroEL's allosteric communication and thermal stability.
- To characterize the functional and conformational properties of wild type GroEL and specific mutants under varying temperatures.
- To determine how electrostatic interactions at inter-ring contact sites influence GroEL's protein substrate binding and temperature sensitivity.
Main Methods:
- Thermal stability assays were performed on wild type GroEL, a single ring mutant (SR1), and two inter-ring salt bridge mutants (E434K, E461K).
- Temperature dependence of functional and conformational properties was analyzed for these GroEL variants.
- Detailed analysis of electrostatic interactions at the inter-ring contact sites was conducted.
Main Results:
- Ionic interactions at inter-ring contact sites are essential for negative cooperativity in protein substrate binding.
- These electrostatic interactions establish the 'protein thermostat' at approximately 39°C.
- Mutations disrupting salt bridges (E434K) reduced thermal stability and altered inactivation kinetics.
- The 'left site' features a more extensive network of electrostatic interactions compared to the 'right site'.
Conclusions:
- Electrostatic interactions, dependent on the number and engagement of residues, stabilize protein-protein interfaces like those in GroEL.
- GroEL utilizes these interactions to distinguish physiological from stress temperatures, regulating its function accordingly.
- The findings highlight the critical role of specific ionic networks in maintaining chaperonin function and cellular thermal homeostasis.