Trans and surface membrane bound zervamicin IIB: 13C-MAOSS-NMR at high spinning speed

Solid-state NMR methods for oriented membrane proteins

Oriented-sample solid-state NMR represents one of few experimental methods capable of characterising the membrane-bound conformation of proteins in the cell membrane. Since the technique was developed 25 years ago, the technique has been applied to study the structure of helix bundle membrane proteins and antimicrobial peptides, characterise protein-lipid interactions, and derive information on dynamics of the membrane anchoring of membrane proteins. We will review the major developments in various aspects of oriented-sample solid-state NMR, including sample-preparation methods, pulse sequences, theory required to interpret the experiments, perspectives for and guidelines to new experiments, and a number of representative applications.

Solvent effects on the secondary structure of the membrane-active zervamicin determined by PELDOR spectroscopy

Zervamicin is a voltage-gated ion-channel-forming peptide. Channels are generally considered to be formed by first insertion of amphipathic molecules into the phospholipid bilayer, followed by self-assembly of a variable number of transmembrane helices. We have studied the length of the peptide structure to address the question whether this peptide is long enough to span the phospholipid bilayer. The pulsed electron-electron double resonance (PELDOR) spectroscopic technique was used to determine the length of the helical molecule in membrane-mimicking solvents. This was achieved from the distance-related dipole-dipole interaction between spin labels, which were located at both ends of the linear peptide chain. The data were obtained by using samples of frozen glassy solutions of MeOH, MeOH/toluene, and MeOH/CHCl(3). Contributions of inter- and intramolecular interactions of spin labels were separated to analyze the intramolecular interaction and the distance distribution function between the labels. It is shown that the main maximum of the distribution functions is located at a distance of ca. 3.3 nm, and this distance appears to be only slightly dependent on the solvent composition. The distribution function was observed to narrow after addition of either CHCl(3) or toluene to MeOH. This effect is rationalized in terms of a decreased mobility of the terminal amino acid residues. By molecular-dynamics simulations, it was shown that the conformation, corresponding with the predominant distance found by PELDOR, agrees well with the mixed alpha/3(10)-helical that was previously determined by NMR. However, in the case toluene was added to the MeOH solution to further increase the hydrophobicity of the environment of the membrane-active peptide, the distribution function gives rise to a minor fraction (7-8%) with a distance of 4.2 nm. This distance corresponds most likely to the more extended 2(7)-helix structure.