Evolution of photosystem I - From symmetry through pseudosymmetry to asymmetry

Adam Ben-Shem, Felix Frolow, Nathan Nelson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

145 Scopus citations


The evolution of photosystem (PS) I was probably initiated by the formation of a homodimeric reaction center similar to the one currently present in green bacteria. Gene duplication has generated a heterodimeric reaction center that subsequently evolved to the PSI present in cyanobacteria, algae and plant chloroplasts. During the evolution of PSI several attempts to maximize the efficiency of light harvesting took place in the various organisms. In the Chlorobiaceae, chlorosomes and FMO were added to the homodimeric reaction center. In cyanobacteria phycobilisomes and CP43′ evolved to cope with the light limitations and stress conditions. The plant PSI utilizes a modular arrangement of membrane light-harvesting proteins (LHCI). We obtained structural information from the two ends of the evolutionary spectrum. Novel features in the structure of Chlorobium tepidum FMO are reported in this communication. Our structure of plant PSI reveals that the addition of subunit G provided the template for LHCI binding, and the addition of subunit H prevented the possibility of trimer formation and provided a binding site for LHCII and the onset of energy spillover from PSII to PSI.

Original languageEnglish
Pages (from-to)274-280
Number of pages7
JournalFEBS Letters
Issue number3
StatePublished - 30 Apr 2004


FundersFunder number
Israel Science Foundation403-02
Israel Science Foundation


    • Evolution
    • Green bacteria
    • Light-harvesting
    • Membrane proteins
    • Photosynthesis
    • Photosystem I


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