4res | pdb_00004res
Crystal structure of the Na,K-ATPase E2P-bufalin complex with bound potassium
Structural highlights
FunctionAT1A1_PIG This is the catalytic component of the active enzyme, which catalyzes the hydrolysis of ATP coupled with the exchange of sodium and potassium ions across the plasma membrane. This action creates the electrochemical gradient of sodium and potassium ions, providing the energy for active transport of various nutrients. Publication Abstract from PubMedCardiotonic steroids (CTSs) are specific and potent inhibitors of the Na(+),K(+)-ATPase, with highest affinity to the phosphoenzyme (E2P) forms. CTSs are comprised of a steroid core, which can be glycosylated, and a varying number of substituents, including a five- or six-membered lactone. These functionalities have specific influence on the binding properties. We report crystal structures of the Na(+),K(+)-ATPase in the E2P form in complex with bufalin (a nonglycosylated CTS with a six-membered lactone) and digoxin (a trisaccharide-conjugated CTS with a five-membered lactone) and compare their characteristics and binding kinetics with the previously described E2P-ouabain complex to derive specific details and the general mechanism of CTS binding and inhibition. CTSs block the extracellular cation exchange pathway, and cation-binding sites I and II are differently occupied: A single Mg(2+) is bound in site II of the digoxin and ouabain complexes, whereas both sites are occupied by K(+) in the E2P-bufalin complex. In all complexes, alphaM4 adopts a wound form, characteristic for the E2P state and favorable for high-affinity CTS binding. We conclude that the occupants of the cation-binding site and the type of the lactone substituent determine the arrangement of alphaM4 and hypothesize that winding/unwinding of alphaM4 represents a trigger for high-affinity CTS binding. We find that the level of glycosylation affects the depth of CTS binding and that the steroid core substituents fine tune the configuration of transmembrane helices alphaM1-2. Structures and characterization of digoxin- and bufalin-bound Na+,K+-ATPase compared with the ouabain-bound complex.,Laursen M, Gregersen JL, Yatime L, Nissen P, Fedosova NU Proc Natl Acad Sci U S A. 2015 Feb 10;112(6):1755-60. doi:, 10.1073/pnas.1422997112. Epub 2015 Jan 26. PMID:25624492[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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