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Fluorescence study on transmembrane Ca2+ gradient-mediated conformation changes of sarcoplasmic reticulum
1National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing, China.
Bioscience Reports
|December 1, 1994
Summary
A calcium gradient across the sarcoplasmic reticulum membrane alters the structure of Ca(2+)-ATPase. This calcium transporter undergoes conformational changes, particularly affecting tryptophan residues at the protein-lipid interface.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Protein Dynamics
Background:
- Sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) actively transports calcium ions.
- Understanding SERCA's conformational changes is crucial for calcium homeostasis.
Purpose of the Study:
- To investigate the conformational states of Ca(2+)-ATPase in response to a transmembrane calcium gradient.
- To identify specific regions within the protein affected by the calcium gradient.
Main Methods:
- Fluorescence spectroscopy to measure intrinsic fluorescence changes.
- Time-resolved fluorescence spectroscopy to analyze tryptophan fluorescence lifetimes.
- Fluorescence quenching using KI and hypocrellin B to probe tryptophan environments.
Main Results:
- An 8% decrease in steady-state fluorescence was observed with a calcium gradient.
- Time-resolved measurements divided 13 tryptophan residues into three groups.
- One tryptophan group showed an increased fluorescence lifetime (5.5 ns to 5.95 ns) in the presence of the gradient.
- Fluorescence quenching indicated dynamic changes in tryptophan residues at the protein-lipid interface.
Conclusions:
- A transmembrane calcium gradient induces significant conformational changes in Ca(2+)-ATPase.
- Specific tryptophan residues, particularly those at the protein-lipid interface, are sensitive to these gradient-mediated structural alterations.
- These findings provide insights into the mechanism of calcium transport and regulation by SERCA.