High-resolution structure of monomeric photosystem I from Thermosynechococcus vestitus
Abstract Photosystem I (PSI) exists in trimeric (tPSI) and monomeric (mPSI) forms within the thylakoid membrane of cyanobacteria. PSI functions as a light-driven electron pump, enabling the transfer of electrons from cytochrome c 6 (Cyt c 6 ) or plastocyanin to ferredoxin. Here, we have developed a novel protocol to obtain large amounts of intact, active mPSI from Thermosynechococcus vestitus ( Tv ) by dissociating highly purified tPSI using the detergent octaethylene glycol monododecyl ether (C 12 E 8 ) at elevated temperatures. We analysed the stability of the protein-detergent complex employing a combination of spectroscopic methods, such as fluorescence at 77 K and circular dichroism (CD), and investigated the detergent’s influence on delipidation and monomerisation. We determined the structure of mPSI to a resolution of 1.8 Å using cryogenic electron microscopy (cryo-EM). This structure retains all subunits except PsaL and we identified a sulfoquinovosyl diacylglycerol (SQD) molecule and 16 n-dodecyl ß-maltoside (βDM) molecules arranged in a ring around the complex. The mPSI structure was verified in solution at physiological temperature by applying small angle neutron scattering. Comparing the cofactor inventory of mPSI to that of tPSI, we suggest the assignment of a red-shifted chlorophyll pigment and discuss the influence of detergents and lipids on stability and oligomeric state of PSI. Finally, when adding native Tv Cyt c 6 under reducing conditions, additional density was observed in close proximity of the P 700 pigments, which indicates the presence of a transiently bound Cyt c 6 .
Authors
- Cecilia Blikstad (ORCID: https://orcid.org/0000-0001-5740-926X)
- Frank Müh (ORCID: https://orcid.org/0000-0002-8818-2616)
- Athina Zouni (ORCID: https://orcid.org/0000-0003-0561-6990)
- Jack A. Forsman (ORCID: https://orcid.org/0000-0002-5111-8901)
- Guillaume Gaullier (ORCID: https://orcid.org/0000-0003-3405-6021)
- Jörg Pieper (ORCID: https://orcid.org/0000-0001-5995-9660)
- Kathleen Wood (ORCID: https://orcid.org/0000-0002-8774-8112)
- Johannes Messinger (ORCID: https://orcid.org/0000-0003-2790-7721)
- Anthony P. Duff (ORCID: https://orcid.org/0000-0003-3586-360X)
- Michael Moir (ORCID: https://orcid.org/0000-0003-1684-3160)
- André T. Graça (ORCID: https://orcid.org/0000-0002-5502-1744)
- Maksym Golub (ORCID: https://orcid.org/0000-0001-5495-9186)
- Nicholas Croy (ORCID: https://orcid.org/0000-0002-1360-0174)
- Jelena Boyka (ORCID: https://orcid.org/0009-0005-3869-7768)
Institutions
- Johannes Kepler University of Linz (AT)
- Uppsala University (SE)
- Australian Nuclear Science and Technology Organisation (AU)
- Humboldt-Universität zu Berlin (DE)
- European Molecular Biology Laboratory (FR)
- Umeå Plant Science Centre (SE)
- Australian Centre for Neutron Scattering (AU)
- National Deuteration Facility (AU)
- University of Tartu (EE)
- University of Otago (NZ)
Publication Details
- Journal
- Photosynthesis Research
- Published
- 2026-10-15
- DOI
- https://doi.org/10.1007/s11120-026-01237-x
- Primary Topic
- Photosynthetic Processes and Mechanisms
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- Australian Nuclear Science and Technology Organisation
- Deutsche Forschungsgemeinschaft
- Svenska Forskningsrådet Formas
- Eesti Teadusagentuur
- Knut och Alice Wallenbergs Stiftelse
- Vetenskapsrådet
- Umeå Universitet
- Uppsala Universitet
- Kempestiftelserna
- Stockholms Universitet
- Center for Exercise Medicine, University of Alabama at Birmingham