Ca2+ regulation of interactions between endoplasmic reticulum chaperones
E F Corbett1, K Oikawa, P Francois
1Medical Research Council of Canada (MRC) Group in Molecular Biology of Membranes, Protein Engineering Network of Centers of Excellence, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
The Journal of Biological Chemistry
|February 26, 1999
Summary
Calcium levels in the endoplasmic reticulum (ER) regulate chaperone interactions. Calreticulin acts as a calcium sensor, controlling the formation and stability of protein complexes essential for protein folding and modification.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Endoplasmic reticulum (ER) lumenal chaperones are crucial for protein folding and quality control.
- Calreticulin, protein disulfide isomerase (PDI), and ERp57 are key ER chaperones involved in these processes.
- Understanding their interactions is vital for elucidating protein homeostasis mechanisms.
Purpose of the Study:
- To investigate the dynamics of interactions between ER lumenal chaperones: calreticulin, PDI, and ERp57.
- To determine the role of calcium (Ca2+) concentration in modulating these chaperone interactions.
- To explore calreticulin's function as a potential Ca2+ sensor.
Main Methods:
- Labeling PDI and ERp57 with the fluorescent dye Casade Blue (CB).
- Monitoring changes in fluorescence intensity of CB-conjugated proteins to detect microenvironment polarity shifts.
- Utilizing Circular Dichroism (CD) analysis to assess protein conformational changes.
- Investigating Ca2+-dependent interactions between calreticulin, PDI, and ERp57.
Main Results:
- Fluorescence intensity changes of CB-PDI and CB-ERp57 correlated with protein conformational alterations.
- PDI interacts with calreticulin at low Ca2+ (<100 μM) and dissociates at high Ca2+ (>400 μM).
- Calreticulin's N-domain interacts with PDI and ERp57; Ca2+ binding to calreticulin's C-domain modulates these interactions.
Conclusions:
- ER lumenal Ca2+ concentration dynamically regulates protein-protein interactions among chaperones.
- Calreticulin functions as a Ca2+ sensor, influencing the formation and stability of chaperone complexes.
- These Ca2+-dependent interactions are critical for protein synthesis, folding, and post-translational modifications within the ER.
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