Mechanism of the E2 to E1 transition in Ca^sup 2+^ pump revealed by crystal structures of gating residue mutants

Ca2+-ATPase of sarcoplasmic reticulum (SERCA1a) pumps two Ca2+ per ATP hydrolyzed from the cytoplasm and two or three protons in the opposite direction. In the E2 state, after transferring Ca2+ into the lumen of sarcoplasmic reticulum, all of the acidic residues that coordinate Ca2+ are thought to b...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 115; no. 50; p. 12722
Main Authors Tsunekawa, Naoki, Ogawa, Haruo, Tsueda, Junko, Akiba, Toshihiko, Toyoshima, Chikashi
Format Journal Article
LanguageEnglish
Published Washington National Academy of Sciences 11.12.2018
Subjects
Adenosine triphosphatase
Ca2+-transporting ATPase
Calcium (reticular)
Calcium ions
Crystal structure
Cytoplasm
Domains
Gating
Mutants
Organic chemistry
Protons
Quantum chemistry
Quantum theory
Sarcoplasmic reticulum
Transmembrane domains
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Summary:Ca2+-ATPase of sarcoplasmic reticulum (SERCA1a) pumps two Ca2+ per ATP hydrolyzed from the cytoplasm and two or three protons in the opposite direction. In the E2 state, after transferring Ca2+ into the lumen of sarcoplasmic reticulum, all of the acidic residues that coordinate Ca2+ are thought to be protonated, including the gating residue Glu309. Therefore a Glu309Gln substitution is not expected to significantly perturb the structure. Here we report crystal structures of the Glu309Gln and Glu309Ala mutants of SERCA1a under E2 conditions. The Glu309Gln mutant exhibits, unexpectedly, large structural rearrangements in both the cytoplasmic and transmembrane domains, apparently uncoupling them. However, the structure definitely represents E2 and, together with the help of quantum chemical calculations, allows us to postulate a mechanism for the E2 → E1 transition triggered by deprotonation of Glu309.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1815472115