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The Structure of Plant Photosystem I – Complexity of the most efficient nano‐photochemical machine in nature
Author(s) -
Nelson Nathan,
Amunts Alexey
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.2_supplement.281
Subject(s) - photosynthetic reaction centre , quantum yield , photosystem i , photosystem ii , chemistry , photosynthesis , photosystem , chloroplast , p700 , crystallography , physics , electron transfer , chemical physics , photochemistry , fluorescence , optics , biochemistry , gene
Plant photosystem I (PSI) is arguably one of the most intricate membrane supercomplexes in nature. It constitutes a reaction center complex (RC) and light‐harvesting complex (LHCI) each composed of quite a few proteins most of which transverse the chloroplast membrane (thylakoid) several times. In addition it contains more than 200 prosthetic groups that is unmatched by any other membrane system. Recently, we have determined the X‐ray crystal structure of PSI from pea plant (Pisum sativum) at 3.4 Å resolution and described a near atomic model of the system. The crystal structure provides a picture at near atomic detail of 11 out of 12 protein subunits of the RC as well as parts of the four subunits of LHCI. The position of 3038 out of 3443 predicted amino acids was assigned. For 2909 of them, side chains were built into the model. At this level, 168 chlorophylls (65 with orientation of the Qx and Qy transition dipolar moments), 2 phylloquinones, 3 Fe4S4 clusters, and 5 carotenoids were described. Plant PSI is the most efficient nano‐photoelectric machine in nature. It is remarkable that PSI with its 200 pigments exhibits a quantum yield of nearly 1, and every captured photon is eventually trapped and results in electron translocation. The structur described in this work provides a first step towards an understanding of how the unprecedented high quantum‐yield of PSI in light capturing and electron transfer is achieved.