Solid-state NMR for the characterization of retinal chromophore and Schiff base in TAT rhodopsin embedded in membranes under weakly acidic conditions.

TAT rhodopsin extracted from the marine bacterium SAR11 HIMB114 has a characteristic Thr-Ala-Thr motif and contains both protonated and deprotonated states of Schiff base at physiological pH conditions due to the low p Here, using solid-state NMR spectroscopy, we investigated the C and N NMR signals of retinal in only the protonated state of TAT in the 1-palmitoyl-2-oleoyl--glycero-3-phosphoethanolamine/1-palmitoyl-2-oleoyl--glycero-3-phospho (1'-rac-glycerol) (POPE/POPG) membrane at weakly acidic conditions. In the C NMR spectrum of C retinal-labeled TAT rhodopsin, the isolated 14-C signals of 13-/15- and 13-/15- isomers were observed at a ratio of 7:3. N retinal protonated Schiff base (RPSB) had a significantly higher magnetic field resonance at 160 ppm.