Structural basis for the photoconversion of a phytochrome to the activated Pfr form

Nature. 2010 Jan 14;463(7278):250-4. doi: 10.1038/nature08671.


Phytochromes are a collection of bilin-containing photoreceptors that regulate numerous photoresponses in plants and microorganisms through their ability to photointerconvert between a red-light-absorbing, ground state (Pr) and a far-red-light-absorbing, photoactivated state (Pfr). Although the structures of several phytochromes as Pr have been determined, little is known about the structure of Pfr and how it initiates signalling. Here we describe the three-dimensional solution structure of the bilin-binding domain as Pfr, using the cyanobacterial phytochrome from Synechococcus OSB'. Contrary to predictions, light-induced rotation of the A pyrrole ring but not the D ring is the primary motion of the chromophore during photoconversion. Subsequent rearrangements within the protein then affect intradomain and interdomain contact sites within the phytochrome dimer. On the basis of our models, we propose that phytochromes act by propagating reversible light-driven conformational changes in the bilin to altered contacts between the adjacent output domains, which in most phytochromes direct differential phosphotransfer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acids / chemistry
  • Amino Acids / metabolism
  • Amino Acids / radiation effects
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / radiation effects*
  • Bile Pigments / chemistry
  • Bile Pigments / metabolism
  • Bile Pigments / radiation effects
  • Binding Sites
  • Light*
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Photoreceptors, Microbial
  • Phytochrome / chemistry*
  • Phytochrome / genetics
  • Phytochrome / metabolism
  • Phytochrome / radiation effects*
  • Protein Kinases / chemistry*
  • Protein Kinases / genetics
  • Protein Kinases / metabolism
  • Protein Kinases / radiation effects*
  • Protein Structure, Tertiary / radiation effects
  • Rotation
  • Synechococcus / chemistry*
  • Synechococcus / genetics


  • Amino Acids
  • Bacterial Proteins
  • Bile Pigments
  • Photoreceptors, Microbial
  • Phytochrome
  • Protein Kinases
  • Cph1 phytochrome protein, bacteria

Associated data

  • PDB/2KLI
  • PDB/2KOI