Resonance Raman Investigation of the Chromophore Structure of Heliorhodopsins

Akihiro Otomo, Misao Mizuno, Manish Singh, Wataru Shihoya, Keiichi Inoue, Osamu Nureki, Oded Beja, Hideki Kandori, Yasuhisa Mizutani

Research output: Contribution to journalArticlepeer-review


Heliorhodopsins (HeRs) are a new category of retinal-bound proteins recently discovered through functional metagenomics analysis that exhibit obvious differences from type-1 microbial rhodopsins. We conducted the first detailed structural characterization of the retinal chromophore in HeRs using resonance Raman spectroscopy. The observed spectra clearly show that the Schiff base of the chromophore is protonated and forms a strong hydrogen bond to a species other than a water molecule, highly likely a counterion residue. The vibrational mode of the Schiff base of HeRs exhibits similarities with that of photosensory microbial rhodopsins, that is consistent with the previous proposal that HeRs function as photosensors. We also revealed unusual spectral features of the in-plane chain vibrations of the chromophore, suggesting an unprecedented geometry of the Schiff base caused by a difference in the retinal pocket structure of HeRs. These data demonstrate structural characteristics of the photoreceptive site in this novel type of rhodopsin family.

Original languageEnglish
Pages (from-to)6431-6436
Number of pages6
JournalJournal of Physical Chemistry Letters
Issue number22
StatePublished - 15 Nov 2018

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Physical and Theoretical Chemistry


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