Cryo-EM structure of photosystem I from the mangrove Avicennia marina under field-grown conditions.

Abstract

Photosystem I (PSI) is a multi-subunit pigment-protein supercomplex that mediates light-driven electron transfer in oxygenic photosynthesis. In this study we investigated whether the photosystem I-light-harvesting complex I (PSI-LHCI) supercomplex from field-grown Avicennia marina preserves canonical angiosperm architecture or exhibits local structural differences, and characterized lipid-mediated interactions that are positioned at several core-antenna interfaces. Here, we present the 2.04 Å cryo-electron microscopy structure of the PSI-LHCI supercomplex from A. marina, a halotolerant mangrove species dominant in the Arabian Gulf and adapted to extreme coastal conditions. This study provides a structural characterization of detergent solubilized, purified PSI-LHCI isolated from field-grown plants exposed to multiple environmental stresses. This work offers a structural baseline and a practical extraction strategy that facilitate the purification of PSI-LHCI from polyphenol-rich, field-collected leaves. The atomic model contains 12 PSI core subunits, four Lhca antenna proteins, 155 chlorophylls, 35 carotenoids, and 19 modeled membrane-associated lipid molecules. Comparisons with other angiosperm PSI-LHCI structures show a largely conserved architecture and conserved lipid binding positions at several core antenna interfaces. However, lipid-mediated contacts at subunit interfaces may contribute to local structural integrity, although their contribution to PSI-LHCI stability under changing salinity remains to be established. These findings may provide a basis for future studies of PSI structure and function under contrasting environmental conditions.

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