Solid-state NMR study of proteorhodopsin in the lipid environment: Secondary structure and dynamics

AbstractProteorhodopsins are typical retinal-binding light-driven proton pumps of heptahelical architecture widely distributed in marine and freshwater bacteria. Recently, we have shown that green proteorhodopsin (GPR) can be prepared in a lipid-bound state that gives well-resolved magic angle spinning (MAS) NMR spectra in samples with different patterns of reverse labelling. Here, we present 3D and 4D sequential chemical shift assignments identified through experiments conducted on a uniformly 13C,15N-labelled sample. These experiments provided the assignments for 153 residues, with a particularly high density in the transmembrane regions (∼74% of residues). The extent of assignments permitted a detailed examination of the secondary structure and dynamics in GPR. In particular, we present experimental evidence of mobility of the protein's termini and of the A–B, C–D, and F–G loops, the latter being possibly coupled to the GPR ion-transporting function