1KJU

Ca2+-ATPase in the E2 State

1KJU の概要

• エントリーDOI: 10.2210/pdb1kju/pdb
• 関連するPDBエントリー: 1EUL
• 分子名称: Sarcoplasmic/endoplasmic reticulum calcium ATPase 1a (1 entity in total)
• 機能のキーワード: ion pump, calcium, membrane protein, p-type atpase, active transport, e2, cryo-em, hydrolase
• 由来する生物種: Oryctolagus cuniculus (rabbit)
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 109602.58

構造登録者

Xu, C.,Rice, W.J.,He, W.,Stokes, D.L. (登録日: 2001-12-05, 公開日: 2001-12-19, 最終更新日: 2024-02-14)

主引用文献

Xu, C.,Rice, W.J.,He, W.,Stokes, D.L.
A structural model for the catalytic cycle of Ca(2+)-ATPase.
J.Mol.Biol., 316:201-211, 2002

PubMed Abstract: Ca(2+)-ATPase is responsible for active transport of calcium ions across the sarcoplasmic reticulum membrane. This coupling involves an ordered sequence of reversible reactions occurring alternately at the ATP site within the cytoplasmic domains, or at the calcium transport sites within the transmembrane domain. These two sites are separated by a large distance and conformational changes have long been postulated to play an important role in their coordination. To characterize the nature of these conformational changes, we have built atomic models for two reaction intermediates and postulated the mechanisms governing the large structural changes. One model is based on fitting the X-ray crystallographic structure of Ca(2+)-ATPase in the E1 state to a new 6 A structure by cryoelectron microscopy in the E2 state. This fit indicates that calcium binding induces enormous movements of all three cytoplasmic domains as well as significant changes in several transmembrane helices. We found that fluorescein isothiocyanate displaced a decavanadate molecule normally located at the intersection of the three cytoplasmic domains, but did not affect their juxtaposition; this result indicates that our model likely reflects a native E2 conformation and not an artifact of decavanadate binding. To explain the dramatic structural effect of calcium binding, we propose that M4 and M5 transmembrane helices are responsive to calcium binding and directly induce rotation of the phosphorylation domain. Furthermore, we hypothesize that both the nucleotide-binding and beta-sheet domains are highly mobile and driven by Brownian motion to elicit phosphoenzyme formation and calcium transport, respectively. If so, the reaction cycle of Ca(2+)-ATPase would have elements of a Brownian ratchet, where the chemical reactions of ATP hydrolysis are used to direct the random thermal oscillations of an innately flexible molecule.

PubMed: 11829513
DOI: 10.1006/jmbi.2001.5330

実験手法

ELECTRON MICROSCOPY (6 Å)