Functional organization of a plant Photosystem I: Evolution of a highly efficient photochemical machine

Alexey Amunts*, Nathan Nelson

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review


Despite its enormous complexity, a plant Photosystem I (PSI) is arguably the most efficient nano-photochemical machine in Nature. It emerged as a homodimeric structure containing several chlorophyll molecules over 3.5 billion years ago, and has perfected its photoelectric properties ever since. The recently determined structure of plant PSI, which is at the top of the evolutionary tree of this kind of complexes, provided the first relatively high-resolution structural model of the supercomplex containing a reaction center (RC) and a peripheral antenna (LHCI) complexes. The RC is highly homologous to that of the cyanobacterial PSI and maintains the position of most transmembrane helices and chlorophylls during 1.5 years of separate evolution. The LHCI is composed of four nuclear gene products (Lhca1-Lhca4) that are unique among the chlorophyll a/b binding proteins in their pronounced long-wavelength absorbance and their assembly into dimers. In this respect, we describe structural elements, which establish the biological significance of a plant PSI and discuss structural variance from the cyanobacterial version. The present comprehensive structural analysis summarizes our current state of knowledge, providing the first glimpse at the architecture of this highly efficient photochemical machine at the atomic level.

Original languageEnglish
Pages (from-to)228-237
Number of pages10
JournalPlant Physiology and Biochemistry
Issue number3
StatePublished - Mar 2008


  • Electron transfer
  • Evolution
  • Light harvesting
  • Photosynthesis
  • Photosystem I
  • Reaction center
  • State transitions


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