The structure of mastoparan-X (MP-X), a G-protein activating peptide from wasp venom, in the state tightly bound to anionic phospholipid bilayers was determined by solid-state NMR spectroscopy. Carbon-13 and nitrogen-15 NMR signals of uniformly labeled MP-X were completely assigned by multidimensional intraresidue C-C, N-CalphaCbeta, and N-Calpha-C', and interresidue Calpha-CalphaCbeta, N-CalphaCbeta, and N-C'-Calpha correlation experiments. The backbone torsion angles were predicted from the chemical shifts of 13C', 13Calpha, 13Cbeta, and 15N signals with the aid of protein NMR database programs. In addition, two 13C-13C and three 13C-15N distances between backbone nuclei were precisely measured by rotational resonance and REDOR experiments, respectively. The backbone structure of MP-X was determined from the 26 dihedral angle restraints and five distances with an average root-mean-square deviation of 0.6 A. Peptide MP-X in the bilayer-bound state formed an amphiphilic alpha-helix for residues Trp3-Leu14 and adopted an extended conformation for Asn2. This membrane-bound conformation is discussed in relation to the peptide's activities to form pores in membranes and to activate G-proteins. This study demonstrates the power of multidimensional solid-state NMR of uniformly isotope-labeled molecules and distance measurements for determining the structures of peptides bound to lipid membranes.

Carbon-13 and nitrogen-15 signals of fully isotope-labeled 15-residue peptide, glycinated mastoparan-X, in a solid state were assigned by two- and three-dimensional NMR experiments under magic-angle spinning conditions. Intra-residue spin connectivities were obtained with multidimensional correlation experiments for C'-C(alpha)-C(beta) and N-C(alpha)-C(beta). Sequence specific assignments were performed with inter-residue C(alpha)-C(alpha) and N-C(alpha)C(beta) correlation experiments. Pulse sequences for these experiments have mixing periods under recoupled zero- and double-quantum (13)C-(13)C and (15)N-(13)C dipolar interactions. These correlation spectra allowed the complete assignments of (13)C and (15)N backbone and (13)C(beta) signals. Chemical shift analysis of the (13)C and (15)N signals based on empirical and quantum chemical databases for proteins indicated that the backbone between residues 3 and 14 forms alpha-helix and residue 2 has extended conformation in the solid state. This structure was compared with the G-protein- and membrane-bound structures of mastoparan-X.

It has been suggested that the hexasome, in which one of the H2A/H2B dimers is depleted from the canonical nucleosome core particle (NCP), is an essential intermediate during NCP assembly and disassembly, but little structural evidence of this exists. In this study, reconstituted products in a conventional NCP preparation were analyzed by native electrospray ionization mass spectrometry, and it was found that the hexasome, which migrated in a manner almost identical to that of the octasome NCP in native polyacrylamide gel electrophoresis, was produced simultaneously with the octasome NCP. This result might contribute to understanding the assembly and disassembly mechanism of NCPs.

FoF1-ATP synthase uses the electrochemical potential across membranes or ATP hydrolysis to rotate the Foc-subunit ring. To elucidate the underlying mechanism, we carried out a structural analysis focused on the active site of the thermophilic c-subunit (TFoc) ring in membranes with a solid-state NMR method developed for this purpose. We used stereo-array isotope labeling (SAIL) with a cell-free system to highlight the target. TFoc oligomers were purified using a virtual ring His tag. The membrane-reconstituted TFoc oligomer was confirmed to be a ring indistinguishable from that expressed in E. coli on the basis of the H(+)-translocation activity and high-speed atomic force microscopic images. For the analysis of the active site, 2D (13)C-(13)C correlation spectra of TFoc rings labeled with SAIL-Glu and -Asn were recorded. Complete signal assignment could be performed with the aid of the C(α)i+1-C(α)i correlation spectrum of specifically (13)C,(15)N-labeled TFoc rings. The C(δ) chemical shift of Glu-56, which is essential for H(+) translocation, and related crosspeaks revealed that its carboxyl group is protonated in the membrane, forming the H(+)-locked conformation with Asn-23. The chemical shift of Asp-61 C(γ) of the E. coli c ring indicated an involvement of a water molecule in the H(+) locking, in contrast to the involvement of Asn-23 in the TFoc ring, suggesting two different means of proton storage in the c rings.

We have developed a solid-state NMR method for observing the signals due to 13C spins of a peptide in the close vicinity of 31P and 2H spins in deuterated phospholipid bilayers. The signal intensities in 13C high-resolution NMR spectra directly indicate the depolarization of 1H by 1H-31P and 1H-2H dipolar couplings under multiple-contact cross-polarization. This method was applied to a fully 13C-, 15N-labeled 14-residue peptide, mastoparan-X (MP-X), bound to phospholipid bilayers whose fatty acyl chains are deuterated. The 13C NMR spectra for the depolarization were simulated from the chemical shifts and structure of membrane-bound MP-X previously determined and the distribution of 2H and 31P spins in lipid bilayers. The minimization of RMSD between the simulated and the experimental spectra showed that the amphiphilic alpha-helix of MP-X was located in the interface between the water layer and the hydrophobic domain of the bilayer, with nonpolar residues facing the phosphorus atoms and alkyl chains of the lipids.

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FF-ATP synthase catalyzes ATP hydrolysis/synthesis coupled with a transmembrane H translocation in membranes. The F c-subunit ring plays a major role in this reaction. We have developed an assignment strategy for solid-state C NMR (ssNMR) signals of the F c-subunit ring of thermophilic Bacillus PS3 (TF c-ring, 72 residues), carrying one of the basic folds of membrane proteins. In a ssNMR spectrum of uniformly C-labeled sample, the signal overlap has been a major bottleneck because most amino acid residues are hydrophobic. To overcome signal overlapping, we developed a method designated as COmplementary Sequential assignment with MInimum Labeling Ensemble (COSMILE). According to this method, we generated three kinds of reverse-labeled samples to suppress signal overlapping. To assign the carbon signals sequentially, two-dimensional C-C'C correlation and dipolar assisted rotational resonance (DARR) experiments were performed under magic-angle sample spinning. On the basis of inter- and intra-residue C-C chemical shift correlations, 97% of C, 97% of C and 92% of C' signals were assigned directly from the spectra. Secondary structure analysis predicted a hairpin fold of two helices with a central loop. The effects of saturated and unsaturated phosphatidylcholines on TF c-ring structure were examined. The DARR spectra at 15 ms mixing time are essentially similar to each other in saturated and unsaturated lipid membranes, suggesting that TF c-rings have similar structures under the different environments. The spectrum of the sample in saturated lipid membranes showed better resolution and structural stability in the gel state. The C-terminal helix was suggested to locate in the outer layer of the c-ring.

The subunit c-ring of H(+)-ATP synthase (F(o) c-ring) plays an essential role in the proton translocation across a membrane driven by the electrochemical potential. To understand its structure and function, we have carried out solid-state NMR analysis under magic-angle sample spinning. The uniformly [(13)C, (15)N]-labeled F(o) c from E. coli (EF(o) c) was reconstituted into lipid membranes as oligomers. Its high resolution two- and three-dimensional spectra were obtained, and the (13)C and (15)N signals were assigned. The obtained chemical shifts suggested that EF(o) c takes on a hairpin-type helix-loop-helix structure in membranes as in an organic solution. The results on the magnetization transfer between the EF(o) c and deuterated lipids indicated that Ile55, Ala62, Gly69 and F76 were lined up on the outer surface of the oligomer. This is in good agreement with the cross-linking results previously reported by Fillingame and his colleagues. This agreement reveals that the reconstituted EF(o) c oligomer takes on a ring structure similar to the intact one in vivo. On the other hand, analysis of the (13)C nuclei distance of [3-(13)C]Ala24 and [4-(13)C]Asp61 in the F(o) c-ring did not agree with the model structures proposed for the EF(o) c-decamer and dodecamer. Interestingly, the carboxyl group of the essential Asp61 in the membrane-embedded EF(o) c-ring turned out to be protonated as COOH even at neutral pH. The hydrophobic surface of the EF(o) c-ring carries relatively short side chains in its central region, which may allow soft and smooth interactions with the hydrocarbon chains of lipids in the liquid-crystalline state.