The cryo-EM structure of Photosystem I from Chromera velia with a bound superoxide dismutase heterodimer
Year: 2025
Type: article
Abstract: Photosystem I is a key component of the solar energy conversion machinery in oxygenic photosynthesis, and its core, where photochemistry occurs, is highly conserved. However, the coral-associated alga Chromera velia that is evolutionary linked to parasitic apicomplexans, exhibits Photosystem I with unusual features. These include the splitting of the central PsaA subunit and the binding of superoxide dismutases as regular subunits. The organization of such a unique Photosystem I was enigmatic. Here, we present the cryo-EM structure of Chromera velia Photosystem I at 1.84 Å resolution. Our work reveals a superoxide dismutase heterodimer bound to the stromal side of the core, stabilized by extensions of canonical subunits, a novel protein PsaV, and a reduced light-harvesting apparatus. We elucidate how the complex evolved to accommodate the superoxide dismutase, assemble the split PsaA, and integrate antenna proteins in a non-canonical orientation. Based on our data and prior physiological data, we propose that this specialized Photosystem I functions likely as an Mehler machine, redirecting electrons from Photosystem II back to water. This mechanism enables Chromera velia to manage redox imbalance and reduce photorespiration through localized oxygen consumption. The alveolate alga Chromera velia is a close relative of parasitic apicomplexans that possesses an unusual Photosystem I. Here, the authors present the cryo-EM structure of this complex, revealing several novel subunits, including a bound superoxide-dismutase heterodimer.
Source: Nature Communications
Authors: Xukun Yuan, Martin Lukeš, Pu Qian, Quentin Charras, Tomáš Smrčka, Petr Man, Lucie Kovářová, Peter Koník, Emmanuel Heilmann, Ashraf Al-Amoudi, Roman Sobotka, Andreas Naschberger
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $6,990
OpenAlex ID: W4417531208