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Real-time identification of two substrate-binding intermediates for the light-driven sodium pump rhodopsin

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Title: Real-time identification of two substrate-binding intermediates for the light-driven sodium pump rhodopsin
Authors: Kato, Tomoya Browse this author
Tsukamoto, Takashi Browse this author →KAKEN DB
Demura, Makoto Browse this author →KAKEN DB
Kikukawa, Takashi Browse this author →KAKEN DB
Issue Date: 18-May-2021
Publisher: American Society for Biochemistry and Molecular Biology
Journal Title: Journal of Biological Chemistry
Volume: 296
Start Page: 100792
Publisher DOI: 10.1016/j.jbc.2021.100792
Abstract: Membrane transport proteins undergo critical conformational changes during substrate uptake and release, as the substrate-binding site is believed to switch its accessibility from one side of the membrane to the other. Thus, at least two substrate-binding intermediates should appear during the process, that is, after uptake and before the release of the substrate. However, this view has not been verified for most transporters because of the difficulty in detecting short-lived intermediates. Here, we report real-time identification of these intermediates for the light-driven outward current-generating Na+-pump rhodopsin. We triggered the transport cycle of Na+-pump rhodopsin using a short laser pulse, and subsequent formation and decay of various intermediates was detected by time-resolved measurements of absorption changes. We used this method to analyze transport reactions and elucidated the sequential formation of the Na+-binding intermediates O1 and O2. Both intermediates exhibited redshifted absorption spectra and generated transient equilibria with short-wavelength intermediates. The equilibria commonly shifted toward O1 and O2 with increasing Na+ concentration, indicating that Na+ is bound to these intermediates. However, these equilibria were formed independently; O1 reached equilibrium with preceding intermediates, indicating Na+ uptake on the cytoplasmic side. In contrast, O2 reached equilibrium with subsequent intermediates, indicating Na+ release on the extracellular side. Thus, there is an irreversible switch in "accessibility" during the O1 to O2 transition, which could represent one of the key processes governing unidirectional Na+ transport.
Type: article
Appears in Collections:国際連携研究教育局 : GI-CoRE (Global Institution for Collaborative Research and Education : GI-CoRE) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)
生命科学院・先端生命科学研究院 (Graduate School of Life Science / Faculty of Advanced Life Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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