The Role of the NDQ Motif in Sodium-Pumping Rhodopsins

Angew Chem Int Ed Engl. 2015 Sep 21;54(39):11536-9. doi: 10.1002/anie.201504549. Epub 2015 Jul 24.


Sodium-pumping rhodopsins (NaRs) are light-driven outward Na(+) pumps. NaRs have a conserved Asn, Asp, and Gln motif (NDQ) in the third transmembrane helix (helix C). The NDQ motif is thus expected to play a crucial role in the operation of the Na(+) pump. Herein, we studied the photocycles of the NDQ-motif mutants of Krokinobacter rhodopsin 2 (KR2), the first discovered NaR, by flash photolysis, to obtain insight into the mechanism of Na(+) transport. For example, the KR2 N112A mutant did not accumulate the transient red-shifted Na(+)-bound state, suggesting that Asn112 is vital for the binding of Na(+) ions. Additionally, Q123A and Q123V mutants showed significantly slower Na(+) uptake and recovery of the initial state. Overall, the Gln123 residue was found to contribute to the optimization of the kinetics of sodium-ion uptake and release. These results demonstrate that the cooperative operation of the three residues of the NDQ motif are important in the operation of the Na(+) pump.

Keywords: kinetics; photolysis; proteins; rhodopsin; sodium pump.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs*
  • Biological Transport
  • Flavobacteriaceae / chemistry*
  • Rhodopsin / chemistry
  • Rhodopsin / metabolism*
  • Sodium / metabolism*
  • Spectrophotometry


  • Rhodopsin
  • Sodium