The Role of the NDQ Motif in Sodium‐Pumping Rhodopsins. Issue 39 (24th July 2015)

• Record Type: Journal Article
• Authors: Inoue, Keiichi; Konno, Masae; Abe‐Yoshizumi, Rei; Kandori, Hideki
• Is Part Of: Angewandte Chemie international edition. Volume 54:Issue 39(2015)
• Page Start: 11536
• Page End: 11539
• Publication Date: 2015-07-24
• Subjects: kinetics -- photolysis -- proteins -- rhodopsin -- sodium pump; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201504549
• Languages: English
• ISSNs: 1433-7851

Abstract

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. Abstract : Ion transport : The conserved NDQ (Asn, Asp, Gln) motif in Krokinobacter rhodopsin 2 (KR2), a novel light‐driven outward Na + pump, is found to play a specific role. The D116 residue receives and sequesters protons for Na + uptake and the uptake process is kinetically optimized by Q123. The N112 residue participates in Na + binding in the O photointermediate. Thus, the NDQ motif works cooperatively for vectorial Na + transport.