Mutant of a Light-Driven Sodium Ion Pump Can Transport Cesium Ions
journal contributionposted on 14.12.2015, 17:09 authored by Masae Konno, Yoshitaka Kato, Hideaki E. Kato, Keiichi Inoue, Osamu Nureki, Hideki Kandori
Krokinobacter eikastus rhodopsin 2 (KR2) is a light-driven Na+ pump found in marine bacterium. KR2 pumps Li+ and Na+, but it becomes an H+ pump in the presence of K+, Rb+, and Cs+. Site-directed mutagenesis of the cytoplasmic surface successfully converted KR2 into a light-driven K+ pump, suggesting that ion selectivity is determined at the cytoplasmic surface. Here we extended this research and successfully created a light-driven Cs+ pump. KR2 N61L/G263F pumps Cs+ as well as other monovalent cations in the presence of a protonophore. Ion-transport activities correlated with the additive volume of the residues at 61 and 263. The result suggests that an ion-selectivity filter is affected by these two residues and functions by strict exclusion of K+ and larger cations in the wild type (N61/G263). In contrast, introduction of large residues possibly destroys local structures of the ion-selectivity filter, leading to the permeation of K+ (P61/W263) and Cs+ (L61/F263).