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Conformational changes of the in situ nuclear pore complex
1Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115 USA.
Biophysical Journal
|July 2, 1999
Summary
Nuclear pore complexes (NPCs) regulate transport between the nucleus and cytoplasm. New atomic force microscopy (AFM) images reveal that a central granule within NPCs changes conformation in response to calcium levels, impacting molecular transport.
Area of Science:
- Cell Biology
- Molecular Biology
- Biophysics
Background:
- Nuclear pore complexes (NPCs) are essential channels facilitating molecular exchange between the cell nucleus and cytoplasm.
- A central structure, known as the nuclear transport protein, central granule, or nuclear plug, has been proposed to regulate the passage of molecules through NPCs.
- Previous visualization techniques, requiring specimen drying and fixation, raised questions about the physiological relevance of observed NPC structures.
Purpose of the Study:
- To visualize nuclear pore complexes (NPCs) and their central granule under more physiological conditions using atomic force microscopy (AFM).
- To investigate the role of calcium (Ca2+) levels in the conformational changes of the NPC's central lumen.
- To determine the physiological relevance of the central granule's gating function in molecular transport.
Main Methods:
- Atomic force microscopy (AFM) was employed to image the outer nuclear membranes and NPCs of Xenopus laevis oocytes.
- Experiments were conducted under varying calcium (Ca2+) depletion conditions to observe NPC behavior.
- In situ imaging allowed for observation of the same NPCs across different solution conditions (control, depletion, repletion).
Main Results:
- AFM imaging under physiological conditions revealed the central granule within NPCs.
- Calcium (Ca2+) depletion led to the central granule occupying and occluding the NPC lumen in over 80% of observed complexes, compared to less than 10% in controls.
- Dynamic imaging demonstrated reversible conformational changes of the NPC central lumen in response to calcium levels.
Conclusions:
- The central lumen of the nuclear pore complex undergoes significant conformational changes.
- These changes are directly influenced by alterations in nuclear cisternal calcium (Ca2+) levels.
- The central granule's dynamic behavior suggests a physiologically relevant mechanism for regulating molecular transport through NPCs.