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Ion Pathways in the Sarcoplasmic Reticulum Ca2+-ATPase.

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Title: Ion Pathways in the Sarcoplasmic Reticulum Ca2+-ATPase.
Authors: Bublitz, Maike1,2 mbu@mb.au.dk, Musgaard, Maria1,3, Poulsen, Hanne1,2, Thøgersen, Lea1,4, Olesen, Claus1,5, Schiøtt, Birgit1,6,7, Preben Morth, J.1,2, Møller, Jesper Vuust1,5, Nissen, Poul1,2
Source: Journal of Biological Chemistry. 4/12/2013, Vol. 288 Issue 15, p10759-10765. 7p.
Subjects: Sarcoplasmic reticulum, Endoplasmic reticulum, Adenosine triphosphatase, Muscle contraction, Bilayer lipid membranes, Ion exchange (Chemistry)
Abstract: The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane ion transporter belonging to the PII-type ATPase family. It performs the vital task of re-sequestering cytoplasmic Ca2+ to the sarco/endoplasmic reticulum store, thereby also terminating Ca2+-induced signaling such as in muscle contraction. This minireview focuses on the transport pathways of Ca2+ and H+ ions across the lipid bilayer through SERCA. The ion-binding sites of SERCA are accessible from either the cytoplasm or the sarco/endoplasmic reticulum lumen, and the Ca2+ entry and exit channels are both formed mainly by rearrangements of four N-terminal transmembrane α-helices. Recent improvements in the resolution of the crystal structures of rabbit SERCA1a have revealed a hydrated pathway in the C-terminal transmembrane region leading from the ionbinding sites to the cytosol. A comparison of different SERCA conformations reveals that this C-terminal pathway is exclusive to Ca2+-free E2 states, suggesting that it may play a functional role in proton release from the ion-binding sites. This is in agreement with molecular dynamics simulations and mutational studies and is in striking analogy to a similar pathway recently described for the related sodium pump. We therefore suggest a model for the ion exchange mechanism in PII-ATPases including not one, but two cytoplasmic pathways working in concert. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane ion transporter belonging to the PII-type ATPase family. It performs the vital task of re-sequestering cytoplasmic Ca2+ to the sarco/endoplasmic reticulum store, thereby also terminating Ca2+-induced signaling such as in muscle contraction. This minireview focuses on the transport pathways of Ca2+ and H+ ions across the lipid bilayer through SERCA. The ion-binding sites of SERCA are accessible from either the cytoplasm or the sarco/endoplasmic reticulum lumen, and the Ca2+ entry and exit channels are both formed mainly by rearrangements of four N-terminal transmembrane α-helices. Recent improvements in the resolution of the crystal structures of rabbit SERCA1a have revealed a hydrated pathway in the C-terminal transmembrane region leading from the ionbinding sites to the cytosol. A comparison of different SERCA conformations reveals that this C-terminal pathway is exclusive to Ca2+-free E2 states, suggesting that it may play a functional role in proton release from the ion-binding sites. This is in agreement with molecular dynamics simulations and mutational studies and is in striking analogy to a similar pathway recently described for the related sodium pump. We therefore suggest a model for the ion exchange mechanism in PII-ATPases including not one, but two cytoplasmic pathways working in concert. [ABSTRACT FROM AUTHOR]
ISSN:00219258
DOI:10.1074/jbc.R112.436550