Probing Membrane Surfaces and the Location of Membrane-Embedded Peptides by C MAS NMR Using Lanthanide Ions

A simple but efficient ¹³C MAS NMR method is presented for the determination of the location of embedded molecules such as peptides relative to biological membrane surfaces by exploiting the interaction with paramagnetic lanthanide ions. Using various aqueous Dy³⁺ concentrations a distance-dependent differential paramagnetic quenching of NMR lipid resonance intensities for specific carbon sites was observed, with residues at the bilayer surface quenched effectively and hydrophobic sites unaffected by Dy³⁺. Tested on the membrane-embedded 50 residue long M13 coat protein, ¹³C labeled at its Val-29 and Val-31 residues, no paramagnetic quenching was observed for the peptide resonances by Dy³⁺, suggesting that Val-29 and Val-31 are not in close proximity to the bilayer interface, but buried deeply inside the hydrophobic region of the lipid bilayer.