PerspectiveStructural Biology

A close view of photosystem I

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Science  29 May 2015:
Vol. 348, Issue 6238, pp. 970-971
DOI: 10.1126/science.aab3387

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Photosystem I (PSI) is an extremely efficient solar energy converter, producing one electron for nearly every photon absorbed (1). This large multipigment-multiprotein complex is an essential constituent of the photosynthetic membrane of plants, algae, and cyanobacteria. The energy of the photons absorbed by the PSI pigments is transferred to chlorophylls in the reaction center, where charge separation occurs. The high chlorophyll concentration in PSI maximizes light harvesting while minimizing the cost of protein synthesis; furthermore, its absorption spectrum is broad and extends to the far-red wavelengths (2). PSI is very stable and only becomes photodamaged in the absence of electron acceptors (3). The structure of the Pisum sativum (pea) PSI at 2.8 Å resolution reported by Qin et al. on page 989 of this issue (4) helps to explain how the pigment-protein complex achieves its remarkable performance.