Diversity of Active States in TMT Opsins

PLoS One. 2015 Oct 22;10(10):e0141238. doi: 10.1371/journal.pone.0141238. eCollection 2015.


Opn3/TMT opsins belong to one of the opsin groups with vertebrate visual and non-visual opsins, and are widely distributed in eyes, brains and other internal organs in various vertebrates and invertebrates. Vertebrate Opn3/TMT opsins are further classified into four groups on the basis of their amino acid identities. However, there is limited information about molecular properties of these groups, due to the difficulty in preparing the recombinant proteins. Here, we successfully expressed recombinant proteins of TMT1 and TMT2 opsins of medaka fish (Oryzias latipes) in cultured cells and characterized their molecular properties. Spectroscopic and biochemical studies demonstrated that TMT1 and TMT2 opsins functioned as blue light-sensitive Gi/Go-coupled receptors, but exhibited spectral properties and photo-convertibility of the active state different from each other. TMT1 opsin forms a visible light-absorbing active state containing all-trans-retinal, which can be photo-converted to 7-cis- and 9-cis-retinal states in addition to the original 11-cis-retinal state. In contrast, the active state of TMT2 opsin is a UV light-absorbing state having all-trans-retinal and does not photo-convert to any other state, including the original 11-cis-retinal state. Thus, TMT opsins are diversified so as to form a different type of active state, which may be responsible for their different functions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Diterpenes
  • Evolution, Molecular
  • Fish Proteins / chemistry*
  • Fish Proteins / metabolism*
  • HEK293 Cells
  • Humans
  • Light*
  • Opsins / chemistry*
  • Opsins / metabolism*
  • Oryzias
  • Phylogeny
  • Recombinant Proteins / metabolism
  • Retinaldehyde / chemistry*
  • Retinaldehyde / metabolism*


  • Diterpenes
  • Fish Proteins
  • Opsins
  • Recombinant Proteins
  • 9-cis-retinal
  • Retinaldehyde

Grant support

This work was supported by Grants-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan to YS (25251036), TY (15H00812 and 25440167) and grants from The Naito Foundation, Mochida Memorial Foundation for Medical and Pharmaceutical Research and The Shimizu Foundation for Immunology and Neuroscience to TY (MEXT: http://www.jsps.go.jp/index.html, Naito Foundation: https://www.naito-f.or.jp/jp/index.php, Mochida Memorial Foundation: http://www.mochida.co.jp/zaidan/, The Shimizu Foundation for Immunology and Neuroscience: http://www.shimizu-immun-neurosci.or.jp/outline/index.html).