Figure 12. Proteolytic cleavage site in the E₁ structure of the Na⁺,K⁺-ATPase.

Architecture of the cytoplasmic loop between membrane spans 6 and 7, as well as the cytoplasmic part of membrane spans 8–10 together with the C-terminal extension in the E₁·AlF₄ ⁻·ADP·3Na⁺ (PDB accession nr 3WGU). The figure was made using Pymol (www.pymol.com). D926, which coordinates Na⁺ in the unique site, is shown in red. Part of the intracellular loop between membrane spans 6 and 7 (L67) is shown. This part contains an asparagine residue (N831, shown in white), cleavage at which produces the C-terminal 19 kDa fragment of the α-subunit [Ref. 38]. Positive amino acids in the C-terminal part of the α-subunit are shown in blue. T₄ indicates the cleavage site described in this study, occurring between R1005 and P1006, as evidenced from Edman degradation. Part of M9, shown in cyan, appears behind M8. The dashed double-headed arrow indicates hypothetical movements of M10 that would result in deflection of the C-terminal tail and consequently modification of the ion binding sites.