Structure and function of wild-type and subunit-depleted photosystem I in Synechocystis

Tirupathi Malavath, Ido Caspy, Sigal Y. Netzer-El, Daniel Klaiman, Nathan Nelson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The ability of photosynthetic organisms to use the sun's light as a sole source of energy sustains life on our planet. Photosystems I (PSI) and II (PSII) are large, multi-subunit, pigment–protein complexes that enable photosynthesis, but this intriguing process remains to be explained fully. Currently, crystal structures of these complexes are available for thermophilic prokaryotic cyanobacteria. The mega-Dalton trimeric PSI complex from thermophilic cyanobacterium, Thermosynechococcus elongatus, was solved at 2.5 Å resolution with X-ray crystallography. That structure revealed the positions of 12 protein subunits (PsaA-F, PsaI-M, and PsaX) and 127 cofactors. Although mesophilic organisms perform most of the world's photosynthesis, no well-resolved trimeric structure of a mesophilic organism exists. Our research model for a mesophilic cyanobacterium was Synechocystis sp. PCC6803. This study aimed to obtain well-resolved crystal structures of [1] a monomeric PSI with all subunits, [2] a trimeric PSI with a reduced number of subunits, and [3] the full, trimeric wild-type PSI complex. We only partially succeeded with the first two structures, but we successfully produced the trimeric PSI structure at 2.5 Å resolution. This structure was comparable to that of the thermophilic species, but we provided more detail. The PSI trimeric supercomplex consisted of 33 protein subunits, 72 carotenoids, 285 chlorophyll a molecules, 51 lipids, 9 iron-sulfur clusters, 6 plastoquinones, 6 putative calcium ions, and over 870 water molecules. This study showed that the structure of the PSI in Synechocystis sp. PCC6803 differed from previously described PSI structures. These findings have broadened our understanding of PSI structure.

Original languageEnglish
Pages (from-to)645-654
Number of pages10
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number9
StatePublished - Sep 2018


FundersFunder number
European Research Council
European Synchrotron Radiation Facility293579 – HOPSEP
Israel Science Foundation569/17
Planning and Budgeting Committee of the Council for Higher Education of Israel1775/12


    • Crystal structure
    • Cyanobacteria
    • Membrane complexes
    • Photosynthesis
    • Photosystem I
    • Synechocystis


    Dive into the research topics of 'Structure and function of wild-type and subunit-depleted photosystem I in Synechocystis'. Together they form a unique fingerprint.

    Cite this