Location and properties of the digitalis receptor site in Na⁺/K⁺‐ATPase

Abstract

Since 1985, several research groups have shown that a number of amino acids in the catalytic a-subunit of Na+/K +-ATPase more or less strongly modulate the affinity of a digitalis compound like ouabain to the enzyme. However, scrutiny of these findings by means of chimeric Na+/K+-ATPase constructs and monoclonal antibodies has recently revealed that the modulatory effect of most of these amino acids does not at all result from direct interaction with ouabain, but rather originates from longrange effects on the properties of the digitalis binding matrix. Starting from this knowledge, the present review brings together the various pieces of evidence pointing to the conclusion that the interface between two interacting a-subunits in the Na+/K+-ATPase protodimer (c~/3)2 provides the cleft for inhibitory digitalis intercalation.Key words: Na+/K+-transporting ATPase; Digitalis receptor; Binding cleft; Location; Property Na*/K+-ATPase is a complex of two catalytic ~-subunits and two catalytically inert fl-subunits, and a number of lipid molecules incorporated into the lipid bilayer of the plasma membrane. The cc-subunit contains about 1,012 amino acids. From the primary sequence, hydropathy analysis has been used to compute the local hydrophobicity and predict single-spanning s-helical segments that are long enough to traverse a 40 membrane (approximately 20 amino acids). The most recent 'working' model of the membrane topology of the enzyme, presented by Askew and Lingrel [14], comprises ten transmembrane segments (H1-H10) linked by five extracellularly disposed loops. Since the membrane topology models are constantly being revised to accommodate new findings, none of the defensible models (cf. Sweadner and Arystarkhova [15]) will be explicitly invoked here. Outcome of various attempts to identify the amino acids involved in the digitalis receptor site

Structural insights into the binding of cardiac glycosides to the digitalis receptor revealed by solid-state NMR

“…The motional restraint experienced by the modified steroid moiety at the binding site might arise from stabilizing hydrogen bond interactions with surface residues (24), constraining interactions with hairpin loops (10), or by intercalation into the protein interior (25). The latter case is unlikely, because raising the temperature by 5°C caused the two-component 2 H NMR line shape in Fig.…”

Thyroid Hormones Stimulate Renal Expression of <i>CFTR</i>

“…Hormones, such as atrial natriuretic peptide (ANP) and aldosterone, can modulate sodium and chloride renal excretion and, consequently, the amount of water in the urine [22,[30][31][32]. Although THs generally are not regarded as classical ECFV regulators, specific receptors for T 3 are present in kidney epithelium, suggesting the potential for a direct hormonal action of this hormone [33].…”

Digitalisforschung in Berlin‐Buch – Rückblick und Ausblick

“…Die membrandurchquerenden Sequenzen H1-H4 tragen die extrazellulir Y' disponierte H1-H2-Verknupfung (QI 11-N122) und H3-H4-Verkniipfung (E307-E312), die bei der Bildung der Digitalis-Erkennungsmatrix und -Bindungsschlucht zusammenzuwirken angenommen wurden [2]. 5.…”