Characterization of retinal chromophore and protonated Schiff base in Thermoplasmatales archaeon heliorhodopsin using
Shibuki Suzuki1, Sari Kumagai1, Toshio Nagashima2
1Graduate School of Engineering Science, Yokohama National University, Yokohama 240-8501, Japan.
Abstract:
Heliorhodopsin (HeR) is a seven-helical transmembrane protein with a retinal chromophore that corresponds to a new rhodopsin family. HeR from the archaebacterium Thermoplasmatales archaeon (TaHeR) exhibits unique features, such as the inverted protein orientation in the membrane compared to other rhodopsins and a long photocycle. Here, we used solid-state nuclear magnetic resonance (NMR) spectroscopy to investigate the 13C and 15N NMR signals of the retinal chromophore and protonated Schiff base (RPSB) in TaHeR embedded in POPE/POPG membrane. Although the 14- and 20-13C retinal signals indicated 13-trans/15-anti (all-trans) configurations, the 20-13C chemical shift value was different from that of other microbial rhodopsins, indicating weakly steric hinderance between Phe203 and the C20 methyl group. 15N RPSB/λmax plot deviated from the linear correlation based on retinylidene-halide model compounds. Furthermore, 15N chemical shift anisotropy (CSA) suggested that Ser112 and Ser234 polar residues distinguish the electronic environment tendencies of RPSB from those of other microbial rhodopsins. Our NMR results revealed that the retinal chromophore and the RPSB in TaHeR exhibit unique electronic environments.
Related Concept Videos
Channel Rhodopsins
Rhodopsins belong to the family of cell surface proteins called G-protein coupled receptors,...
Proton (¹H) NMR: Chemical Shift
Absorption signals of all the protium nuclei...
¹H NMR of Labile Protons: Temporal Resolution
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
¹H NMR of Labile Protons: Deuterium (²H) Substitution


