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A structural model for the catalytic cycle of Ca(2+)-ATPase
Chen Xu1, William J Rice, Wanzhong He
1Skirball Institute for Biomolecular Medicine, Department of Cell Biology, New York University School of Medicine, 540 First Ave, New York, NY, 10016, USA.
Journal of Molecular Biology
|February 7, 2002
Summary
Calcium-transporting ATPase (Ca2+-ATPase) undergoes significant structural changes during calcium ion transport. These movements, driven by ATP hydrolysis and Brownian motion, facilitate ion transport across membranes.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- Ca2+-ATPase actively transports calcium ions across the sarcoplasmic reticulum membrane.
- Coordination between ATP and calcium binding sites involves large conformational changes.
Purpose of the Study:
- To characterize the conformational changes in Ca2+-ATPase during its reaction cycle.
- To build atomic models for reaction intermediates and elucidate mechanisms of structural changes.
Main Methods:
- Fitting X-ray crystallographic structure (E1 state) to cryoelectron microscopy data (E2 state).
- Utilizing fluorescein isothiocyanate to probe decavanadate binding site.
- Developing atomic models for reaction intermediates.
Main Results:
- Calcium binding induces substantial movements in cytoplasmic domains and transmembrane helices.
- A model based on cryo-EM and X-ray data suggests a native E2 conformation.
- Transmembrane helices M4 and M5 are proposed to mediate calcium-binding-induced domain rotation.
Conclusions:
- Ca2+-ATPase conformational changes are crucial for calcium transport.
- The reaction cycle may operate as a Brownian ratchet, utilizing ATP hydrolysis to direct thermal motion.
- The nucleotide-binding and beta-sheet domains are hypothesized to be highly mobile, driven by Brownian motion.