The Role of the NDQ Motif in Sodium-Pumping Rhodopsins.

ABSTRACT: 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.

SUBMITTER: Inoue K 

PROVIDER: S-EPMC4600240 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature