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#Na+/K+ ATPase

14 public questions tagged with this topic.

Membrane Transportation

What is the primary function of Na+/K+ ATPase in maintaining secondary active transport?

Primary role of Na+/K+ ATPase in context of secondary active transport is generation and maintenance of electrochemical sodium gradient that powers numerous symporters and antiporters. By pumping three Na+ outward and two K+ inward per ATP hydrolyzed, it creates chemical gradient low intracellular Na+ and electrical gradient interior negative near minus 70 mV. Combined sodium motive force represents stored free energy. Solute carrier families SLC5 SGLT, SLC6 neurotransmitter transporters, SLC38 amino acid transporters, SLC9 NHE and SLC8 NCX exploit this force allowing Na+ to move downhill whil

Ref: Alberts et al., 7th ed., Chapter 11, Na+/K+ pump and secondary transport coupling.

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Membrane Transportation

What happens if a mutation occurs in the phosphorylation site of Na+/K+ ATPase?

P-type ATPases operate through an ordered Post-Albers cycle involving transient phosphorylation of a conserved aspartate within the DKTGTLT motif of the cytosolic P-domain. ATP phosphorylates this aspartate in E1 state with high Na+ affinity open inward, generating E1-P with occluded Na+, then conversion to E2-P with outward openness and high K+ affinity releases Na+ and binds K+. Dephosphorylation returns enzyme to E2 and E1 states. Phosphorylation triggers long-range movement of nucleotide-binding N domain and actuator A domain, coupling chemical energy to alternating access. A missense or d

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 11, P-type ATPases E1-E2 mechanism.

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Membrane Transportation

The Na+/K+ ATPase pump is essential for:

Na+/K+ ATPase is a heterotetrameric P-type primary active pump that couples ATP hydrolysis to export of three Na+ and import of two K+ per catalytic cycle, maintaining steep ionic gradients of low intracellular Na+ around 12 mM and high K+ around 140 mM. These gradients generate a negative membrane potential and provide chemical potential stored as sodium motive force. Numerous secondary active transporters harness that force rather than ATP directly, including sodium-coupled amino acid transporters SNAT and B0AT systems in intestine and proximal tubule, as well as SGLT1 glucose cotransporters

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Na+-coupled secondary active transport.

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Membrane Transportation

What is the main role of the beta subunit in Na+/K+ ATPase?

Beta subunit of sodium potassium ATPase is glycosylated type two membrane protein about 300 residues containing single membrane span near N terminus and large extracellular domain folded into immunoglobulin-like beta sandwich stabilized by three disulfide bonds and multiple N-linked glycosylation sites required for quality control. Although alpha subunit houses all catalytic motifs nucleotide binding N domain, phosphorylation P domain DKTGTLT aspartate, actuator A domain TGES dephosphorylation, and ion binding residues in M4 M5 M6 M8, beta does not hydrolyze ATP nor bind ions nor form phosphoe

Ref: Geering, J Bioenerg Biomembr, Beta Subunit Roles in Assembly Stability and Trafficking of Na+/K+ ATPase.

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Membrane Transportation

The Na+/K+ ATPase pump is a tetramer consisting of:

Purified sodium potassium ATPase from kidney outer medulla analyzed by SDS PAGE reveals catalytic alpha subunit about 112 kilodaltons with ten membrane spans and beta subunit about 55 kilodaltons glycosylated single pass plus small FXYD regulatory subunit 6 to 10 kilodaltons modulating kinetics. Early radiation inactivation, freeze fracture and crosslinking experiments indicated functional unit larger than heterodimer. Kinetic studies combined with electron microscopy suggested association of two heterodimers. High resolution structures show extracellular domain of beta contacting alpha of sam

Ref: Jorgensen et al., Biochim Biophys Acta, Na+/K+ ATPase Tetrameric Structure 2 Alpha 2 Beta Assembly.

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Membrane Transportation

The Na+/K+ ATPase inhibitor Palytoxin acts by:

Palytoxin ranks among most potent non-protein toxins known, isolated from zoanthid corals Palythoa species, with LD50 subnanomolar due to profound effects on ion homeostasis. Target is Na+/K+ ATPase, P-type pump normally undergoing strict alternating access never simultaneously open both sides. Structural and electrophysiological studies show palytoxin binds extracellular entrance near ouabain site but wedges gates open, stabilizing conformation where intracellular gate formed by M5-M8 and extracellular gate formed by M1-M4 both unlatched, generating continuous pore approximately 13 angstrom d

Ref: Tosteson et al., Palytoxin Converts Na+/K+ ATPase into Non-Selective Ion Channel Mechanism.

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Membrane Transportation

The E2 conformation of Na+/K+ ATPase has:

According to Post-Albers catalytic cycle Na+/K+ ATPase interconverts between E1 inward facing and E2 outward facing with phosphorylated intermediates. In E1 primary sites display high affinity for sodium, three ions bind cytosolic side coordinated by carboxyl side chains and backbone carbonyls accommodating sodium ionic radius 0.95 angstrom. ATP phosphorylates Asp369 generating E1P occluded trapping ions, isomerization to E2P opens outward, sodium affinity drops thousand fold due to rearrangement of M4-M6 helices widening pocket incompatible with high affinity sodium coordination, ions release

Ref: Glynn, J Physiol, Post-Albers Cycle E2 High K+ Affinity Conformation of Na+/K+ ATPase.

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Membrane Transportation

Ouabain is an inhibitor of which ion pump?

Ouabain is a cardenolide steroid with rhamnose sugar derived from Strophanthus and Acocanthera, historically used as arrow poison and experimentally as specific probe. Pharmacologically it exhibits extremely high affinity for extracellular side of Na+/K+ ATPase, nanomolar Ki, interacting with residues in transmembrane helices M1-M6 and extracellular loops forming ouabain binding pocket accessible only in E2P conformation when outward gate open. Binding stabilizes E2P state, prevents dephosphorylation and return to E1, blocking cycle. Resultant inhibition halts sodium extrusion, intracellular s

Ref: Lingrel and Kuntzweiler, JBC, Ouabain Binding Site and Specific Inhibition of Na+/K+ ATPase.

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Membrane Transportation

Which subunit of Na+/K+ ATPase is responsible for ATP hydrolysis?

Na+/K+ ATPase catalytic function resides entirely in alpha subunit approximately 1000 amino acids organized into three cytoplasmic domains and ten transmembrane segments. N domain contains adenine binding pocket including Lys480, Arg544 interacting with ATP ribose and phosphates. P domain harbors DKTGTLT motif where Asp369 undergoes transient phosphorylation receiving gamma phosphate forming energy rich intermediate essential for conformational switching, and TGES motif in A actuator domain mediates dephosphorylation. Ion binding residues Glu327, Glu776, Asp804, Asp808, Thr797 line cavity in M

Ref: Kaplan, Biochemistry of Na+/K+ ATPase, Alpha Subunit Catalytic Domains and ATP Hydrolysis Site.

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Membrane Transportation

The E1 conformation of Na+/K+ ATPase has:

Post-Albers scheme for P-type ATPases defines two principal conformers interconverting via phosphorylation. E1 state is outward closed, inward open, with N domain positioned to accept ATP and transmembrane domain exposing high affinity sodium sites to cytosol. Detailed structures from shark rectal gland enzyme show three sodium ions coordinated by oxygen atoms in pocket formed by M4, M5, M6 and M8 with micromolar affinity at cytosolic concentration about 10 millimolar, while potassium affinity submillimolar low because pocket incompatible with potassium dehydration geometry. Phosphorylation pr

Ref: Albers and Post Model, P-Type Pump Cycle, E1 High Na+ Affinity and E2 High K+ Affinity States.

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Membrane Transportation

The Na+/K+ ATPase pump operates by exchanging:

Active maintenance of sodium and potassium gradients consumes significant portion of cellular ATP budget, about one third in neurons, mediated by Na+/K+ ATPase discovered by Skou. P-type pump cycle begins in E1 conformation with ion binding site open to cytoplasm high affinity for sodium, coordinating three sodium ions using side chain carboxyls of Glu327, Glu776, Asp804 and backbone carbonyls in M4-M6. ATP binds N domain, phosphorylates Asp369 in P domain forming E1P occluded state. Transition to E2P lowers sodium affinity releasing ions extracellularly where sodium about 145 millimolar. Cavi

Ref: Morth et al., Nature 2007, Crystal Structure of Na+/K+ ATPase Stoichiometry 3Na+ Out 2K+ In.

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Membrane Transportation

The Na+/K+ ATPase pump is an example of:

Coupled transporters classified as antiporters exchange substrates in opposite directions driven by gradients. Sodium potassium ATPase exemplifies primary active antiporter using ATP rather than secondary gradient. Alpha subunit has ten transmembrane helices forming pocket with three sodium sites and two potassium sites. It binds three intracellular Na+ in high affinity E1 and exports them while binding two extracellular K+ and importing them, so Na+ and K+ move opposite in same cycle. Exchange is electrogenic due to 3:2 stoichiometry, contributing about minus four millivolts to potential and

Ref: Skou & Esmann, Journal of Bioenergetics 1992: Na+,K+-ATPase as Antiporter Mechanism.

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