Solid-state NMR spectroscopic methods are utilized to study the structure of the membrane protein phospholamban (PLB) and tannins extracted from green tea upon interaction with the lipid bilayer.
The interaction between lipid bilayers and three structurally diverse polyphenols: catechin-(4-8)-catechin-(4-8)-catechin (cat3), (-) epigallocatechin gallate (EGCg) and 1,2,3,4,6-penta-O-galloyl-b-D-glucopyranose (PGG) with varied polarity were examined from the membrane perspective by 31P and 2H solid-state NMR spectroscopy. Direct interaction was observed between the lipid bilayer surface and the most nonpolar PGG, while the most polar cat3 does not have the interaction. The hydrophobic region of the lipid bilayer was dramatically disturbed by PGG, while cat3 did not cause pronounced perturbations. The polarity of the polyphenols affects the interaction with the lipid bilayer. The interactions may relate to the biological activities of polyphenols.
Phospholamban and its phosphorylated (P-PLB) and Arg9Cys mutated (R9C-PLB) forms upon interaction with the lipid bilayer were investigated by 31P and 2H solid-state NMR spectroscopy. Wild-type PLB (WT-PLB) disturbs both the membrane surface and the hydrophobic region dramatically. P-PLB and R9C-PLB have moderate effects on the dynamics of both regions of the lipid bilayer. There is possibly a dissociation process of the PLB cytoplasmic domain from the membrane surface when PLB is phosphorylated or R9C mutated.
WT-PLB, P-PLB and R9C-PLB dynamics, secondary structure and structural topology were investigated and compared utilizing 13C and 15N solid-state NMR spectroscopy. The cytoplasmic domains of P-PLB and R9C-PLB undergo a dissociation process from the membrane surface with a slight population change of the α-helical components and increased backbone dynamics. Upon phosphorylation and R9C mutation, domain Ib shifts from a folded state towards an unfolded state, while the transmembrane domain adopts the same structural conformation. Structural conformation changes of the cytoplasmic domain and domain Ib may lead to PLB inhibitory function relief.