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Photosystem I enters into the spotlight
Plants rely on large complexes of proteins, chlorophyll, and other cofactors to turn light into chemical energy. Qin et al. present the crystal structures of photosystem I (PSI) and the light-harvesting complex I (LHCI) supercomplex from pea plants (see the Perspective by Croce). The well-resolved structure of the outer antenna complexes and their interaction with the PSI core provide a structural basis for calculating excitation energy transfer efficiency. Moreover, the organization and orientation of chlorophyll and carotenoid cofactors within and between PSI and LHCI hint at energy transfer and photoprotection mechanisms.
Photosynthesis converts solar energy to chemical energy by means of two large pigment-protein complexes: photosystem I (PSI) and photosystem II (PSII). In higher plants, the PSI core is surrounded by a large light-harvesting complex I (LHCI) that captures sunlight and transfers the excitation energy to the core with extremely high efficiency. We report the structure of PSI-LHCI, a 600-kilodalton membrane protein supercomplex, from Pisum sativum (pea) at a resolution of 2.8 angstroms. The structure reveals the detailed arrangement of pigments and other cofactors—especially within LHCI—as well as numerous specific interactions between the PSI core and LHCI. These results provide a firm structural basis for our understanding on the energy transfer and photoprotection mechanisms within the PSI-LHCI supercomplex.