Femtosecond-to-millisecond structural changes in a light-driven sodium pump

Petr Skopintsev, David Ehrenberg, Tobias Weinert, Daniel James, Rajiv K. Kar, Philip J.M. Johnson, Dmitry Ozerov, Antonia Furrer, Isabelle Martiel, Florian Dworkowski, Karol Nass, Gregor Knopp, Claudio Cirelli, Christopher Arrell, Dardan Gashi, Sandra Mous, Maximilian Wranik, Thomas Gruhl, Demet Kekilli, Steffen BrünleXavier Deupi, Gebhard F.X. Schertler, Roger M. Benoit, Valerie Panneels, Przemyslaw Nogly, Igor Schapiro, Christopher Milne, Joachim Heberle, Jörg Standfuss*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

110 Scopus citations

Abstract

Light-driven sodium pumps actively transport small cations across cellular membranes1. These pumps are used by microorganisms to convert light into membrane potential and have become useful optogenetic tools with applications in neuroscience. Although the resting state structures of the prototypical sodium pump Krokinobacter eikastus rhodopsin 2 (KR2) have been solved2,3, it is unclear how structural alterations over time allow sodium to be translocated against a concentration gradient. Here, using the Swiss X-ray Free Electron Laser4, we have collected serial crystallographic data at ten pump–probe delays from femtoseconds to milliseconds. High-resolution structural snapshots throughout the KR2 photocycle show how retinal isomerization is completed on the femtosecond timescale and changes the local structure of the binding pocket in the early nanoseconds. Subsequent rearrangements and deprotonation of the retinal Schiff base open an electrostatic gate in microseconds. Structural and spectroscopic data, in combination with quantum chemical calculations, indicate that a sodium ion binds transiently close to the retinal within one millisecond. In the last structural intermediate, at 20 milliseconds after activation, we identified a potential second sodium-binding site close to the extracellular exit. These results provide direct molecular insight into the dynamics of active cation transport across biological membranes.

Original languageAmerican English
Pages (from-to)314-318
Number of pages5
JournalNature
Volume583
Issue number7815
DOIs
StatePublished - 9 Jul 2020

Bibliographical note

Publisher Copyright:
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.

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