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Characterization of the HslU chaperone affinity for HslV protease
M Kamran Azim1, Walter Goehring, Hyun Kyu Song
1Max-Planck-Institut für Biochemie, Martinsried, Germany. kamran.azim@iccs.edu
Protein Science : a Publication of the Protein Society
|April 2, 2005
Summary
The bacterial HslVU protease complex, comprising HslU chaperone and HslV peptidase, forms a stable complex upon substrate binding. This substrate-induced interaction enhances the affinity between HslU and HslV, crucial for protease function.
Area of Science:
- Bacterial Proteases
- Molecular Interactions
- Protein Biochemistry
Background:
- The HslVU complex is a key bacterial ATP-dependent protease.
- It comprises the HslU chaperone and HslV peptidase components.
- Understanding its regulation is vital for bacterial physiology.
Purpose of the Study:
- To investigate the molecular interactions within the Escherichia coli HslVU complex.
- To elucidate the role of protein substrates in modulating HslVU complex stability.
- To characterize the binding affinities between HslU, HslV, and substrate proteins.
Main Methods:
- Surface Plasmon Resonance (SPR) was employed to quantify protein-protein interactions.
- Binding kinetics and affinities were measured for HslU, HslV, and substrate complexes.
- The role of the HslV active site in substrate binding was assessed.
Main Results:
- HslU and HslV exhibit moderate affinity (Kd = 1 µM) for each other.
- Substrate binding (MBP-SulA) to HslU significantly increases HslV affinity (Kd ≈ 0.2 µM), forming a ternary complex.
- HslU strongly binds MBP-SulA (Kd ≈ 10⁻⁹ M), while HslV binds casein (Kd = 0.2 µM) requiring an intact active site.
Conclusions:
- Substrate binding induces a conformational change in HslU, stabilizing the HslVU complex.
- This substrate-induced stabilization is a critical regulatory mechanism for HslVU protease activity.
- The findings highlight the intricate interplay between chaperone, peptidase, and substrate in protease function.