Solid State Nmr Spectroscopic Studies Of Proteins And Small Molecules In Phospholipid Membranes PDF Download

2H, 31P, and 1H-MAS solid-state NMR spectroscopic techniques were used to elucidate the interaction between sorbate, a widely used antibacterial agent, and the lipid bilayers. In the membrane association process, sorbate are most likely interacting with the headgroups, rather than inserting deeply into the acyl chains region. Phospholamban (PLB) regulates calcium transport across the membranes via an inhibitory interaction with SERCA, the cardiac isoform of Ca2+-ATPase. Phosphorylation of PLB relieves the inhibition in a mechanism that is not completely understood. 15N chemical shift changes of ~20 ppm upon phosphorylation were observed in site-specific 15N-labeled PLB and phosphorylated PLB embedded in oriented lipid bilayers, indicating that phosphorylation of PLB alters the structural properties of the cytoplasmic domain with respect to the lipid bilayers. 2H and 15N NMR spectra of wild-type PLB and a N27A PLB mutant reconstituted into lipid bilayers indicate that the N27A mutation does not significantly change the side-chain or backbone dynamics of the transmembrane and cytoplasmic domains. However, dynamic changes are observed for the hinge region, in which greater mobility is observed for the CD3-labeled Ala24 N27A-PLB. This may help to understand why the N27A mutation in the hinge region of PLB leads to heart failures. A new approach for determining the membrane immersion depth of a spin-labeled probe was developed using paramagnetic relaxation enhancement (PRE) in solid-sate NMR spectroscopy. A DOXYL spin label was placed at different depths in the phospholipid bilayers and the resulting enhancements of the 31P spin-lattice relaxation (T1) times were measured and used to calculate the immersion depth. The 31P T1 values decreases steadily as the spin label moves closer to the surface and as the concentration of the spin-labeled lipids increases. These trends of enhanced relaxation vs. the position and the concentration of spin-labels indicate that PRE induced by the DOXYL spin label are significant to determine long distances over the whole depth range of the membranes. This approach may be a powerful biophysical method for measuring membrane protein immersion depth.