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Rescue of Na+ affinity in aspartate 928 mutants of Na+,K+-ATPase by secondary mutation of glutamate 314.

ABSTRACT: The Na(+),K(+)-ATPase binds Na(+) at three transport sites denoted I, II, and III, of which site III is Na(+)-specific and suggested to be the first occupied in the cooperative binding process activating phosphorylation from ATP. Here we demonstrate that the asparagine substitution of the aspartate associated with site III found in patients with rapid-onset dystonia parkinsonism or alternating hemiplegia of childhood causes a dramatic reduction of Na(+) affinity in the ?1-, ?2-, and ?3-isoforms of Na(+),K(+)-ATPase, whereas other substitutions of this aspartate are much less disruptive. This is likely due to interference by the amide function of the asparagine side chain with Na(+)-coordinating residues in site III. Remarkably, the Na(+) affinity of site III aspartate to asparagine and alanine mutants is rescued by second-site mutation of a glutamate in the extracellular part of the fourth transmembrane helix, distant to site III. This gain-of-function mutation works without recovery of the lost cooperativity and selectivity of Na(+) binding and does not affect the E1-E2 conformational equilibrium or the maximum phosphorylation rate. Hence, the rescue of Na(+) affinity is likely intrinsic to the Na(+) binding pocket, and the underlying mechanism could be a tightening of Na(+) binding at Na(+) site II, possibly via movement of transmembrane helix four. The second-site mutation also improves Na(+),K(+) pump function in intact cells. Rescue of Na(+) affinity and Na(+) and K(+) transport by second-site mutation is unique in the history of Na(+),K(+)-ATPase and points to new possibilities for treatment of neurological patients carrying Na(+),K(+)-ATPase mutations.

SUBMITTER: Holm R

PROVIDER: S-EPMC4392278 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Rescue of Na+ affinity in aspartate 928 mutants of Na+,K+-ATPase by secondary mutation of glutamate 314.

Holm Rikke R Einholm Anja P AP Andersen Jens P JP Vilsen Bente B

The Journal of biological chemistry 20150224 15

The Na(+),K(+)-ATPase binds Na(+) at three transport sites denoted I, II, and III, of which site III is Na(+)-specific and suggested to be the first occupied in the cooperative binding process activating phosphorylation from ATP. Here we demonstrate that the asparagine substitution of the aspartate associated with site III found in patients with rapid-onset dystonia parkinsonism or alternating hemiplegia of childhood causes a dramatic reduction of Na(+) affinity in the α1-, α2-, and α3-isoforms ...[more]

PMID: 25713066

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Project description:The neuronal glutamate transporter EAAC1 contains several conserved acidic amino acids in its transmembrane domain, which are possibly important in catalyzing transport and/or binding of co/countertransported cations. Here, we have studied the effects of neutralization by site-directed mutagenesis of three of these amino acid side chains, glutamate 373, aspartate 439, and aspartate 454, on the functional properties of the transporter. Transport was analyzed by whole-cell current recording from EAAC1-expressing mammalian cells after applying jumps in voltage, substrate, or cation concentration. Neutralization mutations in positions 373 and 454, although eliminating steady-state glutamate transport, have little effect on the kinetics and thermodynamics of Na(+) and glutamate binding, suggesting that these two positions do not constitute the sites of Na(+) and glutamate association with EAAC1. In contrast, the D439N mutation resulted in an approximately 10-fold decrease of apparent affinity of the glutamate-bound transporter form for Na(+), and an approximately 2,000-fold reduction in the rate of Na(+) binding, whereas the kinetics and thermodynamics of Na(+) binding to the glutamate-free transporter were almost unchanged compared to EAAC1(WT). Furthermore, the D439N mutation converted l-glutamate, THA, and PDC, which are activating substrates for the wild-type anion conductance, but not l-aspartate, into transient inhibitors of the EAAC1(D439) anion conductance. Activation of the anion conductance by l-glutamate was biphasic, allowing us to directly analyze binding of two of the three cotransported Na(+) ions as a function of time and [Na(+)]. The data can be explained with a model in which the D439N mutation results in a dramatic slowing of Na(+) binding and a reduced affinity of the substrate-bound EAAC1 for Na(+). We propose that the bound substrate controls the rate and the extent of Na(+) interaction with the transporter, depending on the amino acid side chain in position 439.

Dataset Information

Rescue of Na+ affinity in aspartate 928 mutants of Na+,K+-ATPase by secondary mutation of glutamate 314.

Publications

Rescue of Na+ affinity in aspartate 928 mutants of Na+,K+-ATPase by secondary mutation of glutamate 314.

Similar Datasets

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