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PDBsum entry 4ret
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Membrane protein, hydrolase/inhibitor
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PDB id
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4ret
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Contents |
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996 a.a.
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290 a.a.
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32 a.a.
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References listed in PDB file
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Key reference
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Title
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Structures and characterization of digoxin- And bufalin-Bound na+,K+-Atpase compared with the ouabain-Bound complex.
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Authors
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M.Laursen,
J.L.Gregersen,
L.Yatime,
P.Nissen,
N.U.Fedosova.
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Ref.
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Proc Natl Acad Sci U S A, 2015,
112,
1755-1760.
[DOI no: ]
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PubMed id
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Abstract
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Cardiotonic 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, αM4 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 αM4 and hypothesize that
winding/unwinding of αM4 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 αM1-2.
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