Visible-light-induced photodimerization of a photoactive yellow protein (PYP) chromophore model in a single crystal

Naba K. Nath, Kochunnoonny Manoj, Andrei Şerban Gâz, Panče Naumov

Research output: Contribution to journalArticlepeer-review


The chromophore of the photoactive yellow protein (PYP), the photoreceptor in the photomotility of the bacterium Halorhodospira halophila, is a deprotonated para-coumaric thioester linked to the side residue of a cysteine residue. The photophysics of the PYP chromophore is conveniently modeled with para-hydroxycinnamic thiophenyl esters. Herein, we report the first direct evidence, obtained with X-ray diffraction, of photodimerization of a para-hydroxycinnamic thiophenyl ester in single crystalline state. This result represents the first direct observation of [2+2] dimerization of a model PYP chromophore, and demonstrates that even very weak light in the visible region is capable of inducing parallel radical reactions in PYP from the excited state of the chromophore, in addition to the main reaction pathway (trans-cis isomerization). This PYP model system adds an interesting example to the known solid-state photodimerizations, because unlike the anhydrous crystal (which is not capable of sustaining the stress and disintegrates in the course of photodimerization), a single water molecule "dilutes" the structure to the extent sufficient for single-crystal-to-single-crystal reaction. Model under the spotlight: The first X-ray diffraction study of a model for the photoactive yellow protein (PYP) provided direct evidence for the single-crystal-to-single-crystal dimerization of the chromophore under weak visible light (see figure).

Original languageEnglish (US)
Pages (from-to)8094-8099
Number of pages6
JournalChemistry - A European Journal
Issue number25
StatePublished - Jun 17 2013


  • X-ray diffraction
  • dimerization
  • photochemistry
  • proteins
  • solid-state chemistry

ASJC Scopus subject areas

  • General Chemistry
  • Catalysis
  • Organic Chemistry


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