Crystal structure of the potassium-importing KdpFABC membrane complex

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Cellular potassium import is crucial for osmoregulation, pH balance, and membrane potential.
• The bacterial KdpFABC system maintains potassium homeostasis, especially under low-potassium conditions.

Purpose of the Study:

• To elucidate the mechanism of uphill potassium transport coupled with ATP hydrolysis in the KdpFABC complex.
• To determine the X-ray structure of the complete Escherichia coli KdpFABC complex.

Main Methods:

• X-ray crystallography at 2.9 Å resolution.
• Structural analysis of the KdpFABC complex.

Main Results:

• The structure reveals a potassium ion in KdpA's selectivity filter and a water molecule in KdpB's transmembrane domain.
• Identified a protein-embedded tunnel connecting KdpA and KdpB.
• Discovered a helix in KdpA linked to KdpB's phosphorylation domain, suggesting a coupling mechanism.

Conclusions:

• Proposed a novel mechanism for active transport by repurposing protein channel architecture.
• The findings provide insights into the coupling of ion transport and ATP hydrolysis.