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Structural basis for potassium transport in prokaryotes by KdpFABC
Marie E Sweet1, Casper Larsen2, Xihui Zhang1
1Skirball Institute of Biomolecular Medicine, Department of Cell Biology, New York University Grossman School of Medicine, New York, NY 10016.
Summary
The KdpFABC complex transports potassium ions in prokaryotes. Cryo-EM structures reveal a static KdpA channel and dynamic KdpB pump, detailing the K+ transport pathway and mechanism.
Area of Science:
- Structural Biology
- Biochemistry
- Molecular Biology
Background:
- The KdpFABC complex is crucial for maintaining ionic homeostasis in prokaryotes under stress.
- It consists of a K+ channel (KdpA) and a P-type ATPase (KdpB).
- Previous structural studies proposed conflicting transport mechanisms.
Purpose of the Study:
- To elucidate the transport mechanism of the KdpFABC complex.
- To resolve contradictory hypotheses regarding its function.
- To visualize key intermediates in the K+ transport cycle.
Main Methods:
- Cryogenic electron microscopy (cryo-EM) was used to determine structures.
- Substrate analogs were employed to stabilize four key reaction intermediates.
- Structural analysis focused on conformational changes and ion pathways.
Main Results:
- Structures revealed static KdpA, KdpC, and KdpF subunits, with dynamic KdpB.
- Spherical densities identified as K+ or water define a transport pathway.
- The pathway involves an intramembrane tunnel in KdpA delivering ions to KdpB.
Conclusions:
- A mechanism is proposed where ATP hydrolysis drives K+ transfer within KdpB.
- Ions are delivered to a low-affinity site for cytoplasmic release.
- This study provides atomic-level insight into prokaryotic potassium transport.