A common ancestor for oxygenic and anoxygenic photosynthetic systems: A comparison based on the structural model of photosystem I

Wolf Dieter Schubert, Olaf Klukas, Wolfram Saenger, Horst Tobias Witt, Petra Fromme, Norbert Krauß

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183 Scopus citations


The 4 Å structural model of photosystem I (PSI) has elucidated essential features of this protein complex. Inter alia, it demonstrates that the core proteins of PSI, PsaA and PsaB each consist of an N-terminal antenna-binding domain, and a C-terminal reaction center (RC)-domain. A comparison of the PC-domain of PSI and the photosynthetic RC of purple bacteria (PbRC), reveals significantly analogous structures. This provides the structural support for the hypothesis that the two RC-types (I and II) share a common evolutionary origin. Apart from a similar set of constituent cofactors of the electron transfer system, the analogous features include a comparable cofactor arrangement and a corresponding secondary structure motif of the RC-cores. Despite these analogies, significant differences are evident, particularly as regards the distances between and the orientation of individual cofactors, and the length and orientation of α-helices. Inferred roles of conserved amino acids are discussed for PSI, photosystem II (PSII), photosystem C (PSC, green sulfur bacteria) and photosystem H (PSH, heliobacteria). Significant sequence homology between the N-terminal, antenna-binding domains of the core proteins of type-I RCs, PsaA, PsaB, PscA and PshA (of PSI, PSC and PSH respectively) with the antenna-binding subunits CP43 and CP47 of PSII indicate that PSII has a modular structure comparable to that of PSI.

Original languageEnglish (US)
Pages (from-to)297-314
Number of pages18
JournalJournal of Molecular Biology
Issue number2
Publication statusPublished - Jul 10 1998
Externally publishedYes



  • Green sulfur bacteria
  • Heliobacteria
  • Photosynthetic reaction centers
  • Photosystem I and photosystem II
  • Purple bacteria

ASJC Scopus subject areas

  • Virology

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