SERCA mutant E309Q binds two Ca ions but adopts a catalytically incompetent conformation

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The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) couples ATP hydrolysis to transport of Ca2+. This directed energy transfer requires cross-talk between the two Ca2+ sites and the phosphorylation site over 50 A distance. We have addressed the mechano-structural basis for this intramolecular signal by analysing the structure and the functional properties of SERCA mutant E309Q. Glu309 contributes to Ca2+ coordination at site II, and a consensus has been that E309Q only binds Ca2+ at site I. The crystal structure of E309Q in the presence of Ca2+ and an ATP analogue, however, reveals two occupied Ca2+ sites of a non-catalytic Ca2E1 state. Ca2+ is bound with micromolar affinity by both Ca2+ sites in E309Q, but without cooperativity. The Ca2+-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 Ca2+ site II
TidsskriftE M B O Journal
Sider (fra-til)3231-3243
Antal sider13
StatusUdgivet - 11 dec. 2013

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