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PDBsum entry 4nab
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References listed in PDB file
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Key reference
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Title
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Serca mutant e309q binds two ca(2+) ions but adopts a catalytically incompetent conformation.
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Authors
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J.D.Clausen,
M.Bublitz,
B.Arnou,
C.Montigny,
C.Jaxel,
J.V.Møller,
P.Nissen,
J.P.Andersen,
M.Le maire.
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Ref.
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Embo J, 2013,
32,
3231-3243.
[DOI no: ]
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PubMed id
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Abstract
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The sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) couples ATP hydrolysis to
transport of Ca(2+). This directed energy transfer requires cross-talk between
the two Ca(2+) sites and the phosphorylation site over 50 Å distance. We have
addressed the mechano-structural basis for this intramolecular signal by
analysing the structure and the functional properties of SERCA mutant E309Q.
Glu(309) contributes to Ca(2+) coordination at site II, and a consensus has been
that E309Q only binds Ca(2+) at site I. The crystal structure of E309Q in the
presence of Ca(2+) and an ATP analogue, however, reveals two occupied Ca(2+)
sites of a non-catalytic Ca2E1 state. Ca(2+) is bound with micromolar affinity
by both Ca(2+) sites in E309Q, but without cooperativity. The Ca(2+)-bound
mutant does phosphorylate from ATP, but at a very low maximal rate.
Phosphorylation depends on the correct positioning of the A-domain, requiring a
shift of transmembrane segment M1 into an 'up and kinked position'. This
transition is impaired in the E309Q mutant, most likely due to a lack of charge
neutralization and altered hydrogen binding capacities at Ca(2+) site II.
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