TY  - JOUR
A1  - Dürr, Katharina L.
A1  - Tavraz, Neslihan Neslihan
A1  - Dempski, Robert E.
A1  - Bamberg, Ernst
A1  - Friedrich, Thomas
T1  - Functional significance of E2 state stabilization by specific α/β-subunit interactions of Na,K- and H,K-ATPase
T2  - Journal of biological chemistry
N2  - The β-subunits of Na,K-ATPase and H,K-ATPase have important functions in maturation and plasma membrane targeting of the catalytic α-subunit but also modulate the transport activity of the holoenzymes. In this study, we show that tryptophan replacement of two highly conserved tyrosines in the transmembrane domain of both Na,K- and gastric H,K-ATPase β-subunits resulted in considerable shifts of the voltage-dependent E1P/E2P distributions toward the E1P state as inferred from presteady-state current and voltage clamp fluorometric measurements of tetramethylrhodamine-6-maleimide-labeled ATPases. The shifts in conformational equilibria were accompanied by significant decreases in the apparent affinities for extracellular K+ that were moderate for the Na,K-ATPase β-(Y39W,Y43W) mutation but much more pronounced for the corresponding H,K-ATPase β-(Y44W,Y48W) variant. Moreover in the Na,K-ATPase β-(Y39W,Y43W) mutant, the apparent rate constant for reverse binding of extracellular Na+ and the subsequent E2P-E1P conversion, as determined from transient current kinetics, was significantly accelerated, resulting in enhanced Na+ competition for extracellular K+ binding especially at extremely negative potentials. Analogously the reverse binding of extracellular protons and subsequent E2P-E1P conversion was accelerated by the H,K-ATPase β-(Y44W,Y48W) mutation, and H+ secretion was strongly impaired. Remarkably tryptophan replacements of residues in the M7 segment of Na,K- and H,K-ATPase α-subunits, which are at interacting distance to the β-tyrosines, resulted in similar E1 shifts, indicating their participation in stabilization of E2. Thus, interactions between selected residues within the transmembrane regions of α- and β-subunits of P2C-type ATPases exert an E2-stabilizing effect, which is of particular importance for efficient H+ pumping by H,K-ATPase under in vivo conditions.
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/76436
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-764368
SN  - 0021-9258
VL  - 284.2009
IS  - 6
SP  - 3842
EP  - 3854
PB  - American Society for Biochemistry and Molecular Biology Publications
CY  - Bethesda, Md
ER  -