Molecular Mechanisms of Photoadaptation of Photosystem I Supercomplex from an Evolutionary Cyanobacterial/Algal Intermediate

Plant Physiol. 2018 Feb;176(2):1433-1451. doi: 10.1104/pp.17.01022. Epub 2017 Nov 29.


The monomeric photosystem I-light-harvesting antenna complex I (PSI-LHCI) supercomplex from the extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction center and its green algal/higher plant counterpart. We show that the C. merolae PSI-LHCI supercomplex is characterized by robustness in various extreme conditions. By a combination of biochemical, spectroscopic, mass spectrometry, and electron microscopy/single particle analyses, we dissected three molecular mechanisms underlying the inherent robustness of the C. merolae PSI-LHCI supercomplex: (1) the accumulation of photoprotective zeaxanthin in the LHCI antenna and the PSI reaction center; (2) structural remodeling of the LHCI antenna and adjustment of the effective absorption cross section; and (3) dynamic readjustment of the stoichiometry of the two PSI-LHCI isomers and changes in the oligomeric state of the PSI-LHCI supercomplex, accompanied by dissociation of the PsaK core subunit. We show that the largest low light-treated C. merolae PSI-LHCI supercomplex can bind up to eight Lhcr antenna subunits, which are organized as two rows on the PsaF/PsaJ side of the core complex. Under our experimental conditions, we found no evidence of functional coupling of the phycobilisomes with the PSI-LHCI supercomplex purified from various light conditions, suggesting that the putative association of this antenna with the PSI supercomplex is absent or may be lost during the purification procedure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Biological
  • Chlorophyll / metabolism
  • Circular Dichroism
  • Cyanobacteria / chemistry
  • Cyanobacteria / physiology
  • Evolution, Molecular
  • Hydrogen-Ion Concentration
  • Light
  • Light-Harvesting Protein Complexes / chemistry*
  • Light-Harvesting Protein Complexes / metabolism*
  • Photosystem I Protein Complex / chemistry*
  • Photosystem I Protein Complex / metabolism*
  • Rhodophyta / chemistry
  • Rhodophyta / physiology*
  • Spectrometry, Fluorescence
  • Temperature
  • Zeaxanthins / metabolism


  • Light-Harvesting Protein Complexes
  • Photosystem I Protein Complex
  • Zeaxanthins
  • Chlorophyll