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Contents 1 Introduction to Sodium-Potassium-ATPases 2 Structure 2.1 α-Subunit 2.2 β-subunit 3 References

Introduction to Sodium-Potassium-ATPases

The sodium-potassium-ATPase, also known as the Na⁺-K⁺ pump is the protein responsible for the ATP-dependent coupled transport of sodium and potassium ions across the plasma membrane. The Na⁺-K⁺ pump is found in all animal cells and is a major force in maintaining the concentration gradients of these ions across the membrane. These gradients provide energy for several cellular functions including control of membrane potential, cell size, and pH homeostasis, and nutrient uptake. Each cycle of ATP hydrolysis, the protein transports three Na⁺ ions out of the cell and two K⁺ ions across the plasma membrane into the cell. In addition to its role as a transport protein, the sodium-potassium-pump has also been shown to act as a receptor for cardiotonic steroid signalling.

Structure

spinqualitylabelsall models The Na-K Pump; α-subunit in blue, β-subunit in green, and FXYD subunit in yellow. Oriented with the cytoplasmic face up. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

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The Na⁺-K⁺ pump is a P-type ATPase with a structure similar to the H⁺-K⁺-ATPase[1] and the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA)[2]. Overall, the structure of the sodium-potassium-pump is a transmembrane protein with three subunits labeled α, β, and FXYD.

α-Subunit

The α-subunit is the largest subunit and contains the binding sites for Na⁺, K⁺, and ATP. This subunit is composed of 10 transmembrane α-helices (M1-M10). These helices are centered around a three helix bundle formed by M4-M6. The binding sites for K⁺ and Na⁺ are located within the transmembrane helices. Additionally, there are located on the cytoplasmic face of the membrane: the actuator domain (A), the nucleotide-binding domain (N), and the phosphorylation domain (P).

β-subunit

The β-subunit is a single spanning membrane protein with a transmembrane α-helix and a glycosylated extracellular domain. This subunit is bound by hydrogen bonds and numerous hydrophobic contacts from a to M7 and M10 helices of the α-subunit. These residues also make contact with a cholesterol molecule that is necessary for ion transport to occur. It has important roles in targeting the protein to the membrane and providing stability. It also has a role in providing binding specificity for potassium ions.

References