Structural adaptations of photosynthetic complex I enable ferredoxin-dependent electron transfer

Science. 2019 Jan 18;363(6424):257-260. doi: 10.1126/science.aau3613. Epub 2018 Dec 20.


Photosynthetic complex I enables cyclic electron flow around photosystem I, a regulatory mechanism for photosynthetic energy conversion. We report a 3.3-angstrom-resolution cryo-electron microscopy structure of photosynthetic complex I from the cyanobacterium Thermosynechococcus elongatus. The model reveals structural adaptations that facilitate binding and electron transfer from the photosynthetic electron carrier ferredoxin. By mimicking cyclic electron flow with isolated components in vitro, we demonstrate that ferredoxin directly mediates electron transfer between photosystem I and complex I, instead of using intermediates such as NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate). A large rate constant for association of ferredoxin to complex I indicates efficient recognition, with the protein subunit NdhS being the key component in this process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • Cyanobacteria / physiology*
  • Electron Transport
  • Electron Transport Complex I / physiology*
  • Ferredoxins / physiology*
  • Models, Molecular
  • Photosynthesis*
  • Photosystem I Protein Complex / physiology*
  • Protein Structure, Quaternary


  • Ferredoxins
  • Photosystem I Protein Complex
  • Electron Transport Complex I