Structural basis for Na(+) transport mechanism by a light-driven Na(+) pump

Nature. 2015 May 7;521(7550):48-53. doi: 10.1038/nature14322. Epub 2015 Apr 6.


Krokinobacter eikastus rhodopsin 2 (KR2) is the first light-driven Na(+) pump discovered, and is viewed as a potential next-generation optogenetics tool. Since the positively charged Schiff base proton, located within the ion-conducting pathway of all light-driven ion pumps, was thought to prohibit the transport of a non-proton cation, the discovery of KR2 raised the question of how it achieves Na(+) transport. Here we present crystal structures of KR2 under neutral and acidic conditions, which represent the resting and M-like intermediate states, respectively. Structural and spectroscopic analyses revealed the gating mechanism, whereby the flipping of Asp116 sequesters the Schiff base proton from the conducting pathway to facilitate Na(+) transport. Together with the structure-based engineering of the first light-driven K(+) pumps, electrophysiological assays in mammalian neurons and behavioural assays in a nematode, our studies reveal the molecular basis for light-driven non-proton cation pumps and thus provide a framework that may advance the development of next-generation optogenetics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Crystallography, X-Ray
  • Flavobacteriaceae / chemistry*
  • Hydrogen-Ion Concentration
  • Ion Pumps / chemistry*
  • Ion Pumps / genetics
  • Ion Pumps / metabolism
  • Ion Pumps / radiation effects*
  • Ion Transport / genetics
  • Ion Transport / radiation effects
  • Light*
  • Models, Biological
  • Models, Molecular
  • Mutagenesis / genetics
  • Optogenetics
  • Potassium / metabolism
  • Protein Conformation
  • Protein Engineering
  • Retinaldehyde / chemistry
  • Retinaldehyde / metabolism
  • Rhodopsin / chemistry*
  • Rhodopsin / genetics
  • Rhodopsin / metabolism
  • Rhodopsin / radiation effects*
  • Schiff Bases
  • Sodium / metabolism*
  • Structure-Activity Relationship


  • Ion Pumps
  • Schiff Bases
  • Rhodopsin
  • Sodium
  • Retinaldehyde
  • Potassium

Associated data

  • PDB/3X3B
  • PDB/3X3C