Sequence-specific 1H NMR assignments and secondary structure of the streptococcal protein G B2-domain.

Two-dimensional NMR spectroscopy has been used to obtain sequence-specific 1H NMR assignments for the IgG-binding B2-domain of streptococcal protein G. Secondary structure elements were identified from analysis of characteristic backbone-backbone NOE patterns and amide proton exchange data. The B2-domain contains a four-stranded beta-sheet region in which the two inner strands form a parallel beta-sheet with each other and antiparallel beta-sheets with the outer strands. The outer strands are connected via a 16-residue alpha-helix and short loops on both ends of the helix. The alpha-helix and beta-sheet structures contain well-defined polar and apolar sides, and numerous long-range NOEs from the apolar helix to apolar sheet regions were used to derive a model for the global fold of the B2-domain. While the overall fold is similar to that obtained for B1-type domains, differences in amide proton exchange rates and hydrophobic packing are observed.     

NMR studies of amyloid beta-peptides: proton assignments, secondary structure, and mechanism of an alpha-helix----beta-sheet conversion for a homologous, 28-residue, N-terminal fragment.

Beta-peptide is a major component of amyloid deposits in Alzheimer's disease. We report here a proton nuclear magnetic resonance (NMR) spectroscopic investigation of a synthetic peptide that is homologous to residues 1-28 of beta-peptide [abbreviated as beta-(1-28)]. The beta-(1-28) peptide produces insoluble beta-pleated sheet structures in vitro, similar to the beta-pleated sheet structures of beta-peptide in amyloid deposits in vivo. For peptide solutions in the millimolar range, in aqueous solution at pH 1-4 the beta-(1-28) peptide adopts a monomeric random coil structure, and at pH 4-7 the peptide rapidly precipitates from solution as an oligomeric beta-sheet structure, analogous to amyloid deposition in vivo. The NMR work shown here demonstrates that the beta-(1-28) peptide can adopt a monomeric alpha-helical conformation in aqueous trifluoroethanol solution at pH 1-4. Assignment of the complete proton NMR spectrum and the determination of the secondary structure were arrived at from interpretation of two-dimensional (2D) NMR data, primarily (1) nuclear Overhauser enhancement (NOE), (2) vicinal coupling constants between the amide (NH) and alpha H protons, and (3) temperature coefficients of the NH chemical shifts. The results show that at pH 1.0 and 10 degrees C the beta-(1-28) peptide adopts an alpha-helical structure that spans the entire primary sequence. With increasing temperature and pH, the alpha-helix unfolds to produce two alpha-helical segments from Ala2 to Asp7 and Tyr10 to Asn27. Further increases in temperature to 35 degrees C cause the Ala2-Asp7 section to become random coil, while the His13-Phe20 section stays alpha-helical. A mechanism involving unfavorable interactions between charged groups and the alpha-helix macrodipole is proposed for the alpha-helix----beta-sheet conversion observed at midrange pH.     

Aromatic interactions in model peptide β-hairpins: ring current effects on proton chemical shifts

Crystal structures of eight peptide β-hairpins in the sequence Boc-Leu-Phe-Val-Xxx-Yyy-Leu-Phe-Val-OMe revealed that the Phe(2) and Phe(7) aromatic rings are in close spacial proximity, with the centroid-centroid distance (R(cen)) of 4.4-5.4 ? between the two phenyl rings. Proton NMR spectra in chloroform and methanol solution reveal a significant upfield shift of the Phe(7) C(δ,δ') H(2) protons (6.65-7.04 ppm). Specific assignments of the aromatic protons have been carried out in the peptide Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe (6). The anticipated ring current shifts have been estimated from the aromatic ring geometrics observed in crystals for all eight peptides. Only one of the C(δ,δ') H proton lies in the shielding zone with rapid ring flipping, resulting in averaging between the two extreme chemical shifts. An approximate estimate of the population of conformations, which resemble crystal state orientation, may be obtained. Key nuclear Overhauser effects (NOEs) between facing Phe side chains provide support for close similarity between the solid state and solution conformation. Temperature dependence of aromatic ring proton chemical shift and line widths for peptide 6 (Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe) and the control peptide Boc-Leu-Val-Val-(D)Pro-Gly-Leu-Phe-Val-OMe establish an enhanced barrier to ring flipping when the two Phe rings are in proximity. Modeling studies suggest that small, conformational adjustment about C(α)-C(β) (χ(1) ) and C(β)-C(γ) (χ(2) ) bonds of both the Phe residues may be required in order to permit unhindered, uncorrelated flipping of both the Phe rings. The maintenance of the specific aromatic ring orientation in organic solvents provides evidence for significant stabilizing interaction.     

A recipe for designing water-soluble, beta-sheet-forming peptides.

Based on observations of solubility and folding properties of peptide 33-mers derived from the beta-sheet domains of platelet factor-4 (PF4), interleukin-8 (IL-8), and growth related protein (Gro-alpha), as well as other beta-sheet-forming peptides, general guidelines have been developed to aid in the design of water soluble, self-association-induced beta-sheet-forming peptides. CD, 1H-NMR, and pulsed field gradient NMR self-diffusion measurements have been used to assess the degree of folding and state of aggregation. PF4 peptide forms native-like beta-sheet tetramers and is sparingly soluble above pH 6. IL-8 peptide is insoluble between pH 4.5 and pH 7.5, yet forms stable, native-like beta-sheet dimers at higher pH. Gro-alpha peptide is soluble at all pH values, yet displays no discernable beta-sheet structure even when diffusion data indicate dimer-tetramer aggregation. A recipe used in the de novo design of water-soluble beta-sheet-forming peptides calls for the peptide to contain 40-50% hydrophobic residues, usually aliphatic ones (I, L, V, A, M) (appropriately paired and mostly but not always alternating with polar residues in the sheet sequence), a positively charged (K, R) to negatively charged (E, D) residue ratio between 4/2 and 6/2, and a noncharged polar residue (N, Q, T, S) composition of about 20% or less. Results on four de novo designed, 33-residue peptides are presented supporting this approach. Under near physiologic conditions, all four peptides are soluble, form beta-sheet structures to varying degrees, and self-associate. One peptide folds as a stable, compact beta-sheet tetramer, whereas the others are transient beta-sheet-containing aggregates.     

Solution structure of PAFP-S: a new knottin-type antifungal peptide from the seeds of Phytolacca americana

The three-dimensional solution structure of PAFP-S, an antifungal peptide extracted from the seeds of Phytolacca americana, was determined using 1H NMR spectroscopy. This cationic peptide contains 38 amino acid residues. Its structure was determined from 302 distance restraints and 36 dihedral restraints derived from NOEs and coupling constants. The peptide has six cysteines involved in three disulfide bonds. The previously unassigned parings have now been determined from NMR data. The solution structure of PAFP-S is presented as a set of 20 structures using ab initio dynamic simulated annealing, with an average RMS deviation of 1.68 A for the backbone heavy atoms and 2.19 A for all heavy atoms, respectively. For the well-defined triple-stranded beta-sheet involving residues 8-10, 23-27, and 32-36, the corresponding values were 0.39 and 1.25 A. The global fold involves a cystine-knotted three-stranded antiparallel beta-sheet (residues 8-10, 23-27, 32-36), a flexible loop (residues 14-19), and four beta-reverse turns (residues 4-8, 11-14, 19-22, 28-32). This structure features all the characteristics of the knottin fold. It is the first structural model of an antifungal peptide that adopts a knottin-type structure. PAFP-S has an extended hydrophobic surface comprised of residues Tyr23, Phe25, Ile27, Tyr32, and Val34. The side chains of these residues are well-defined in the NMR structure. Several hydrophilic and positively charged residues (Arg9, Arg38, and Lys36) surround the hydrophobic surface, giving PAFP-S an amphiphilic character which would be the main structural basis of its biological function.     

Solution structure of the phosphocarrier protein HPr from Bacillus subtilis by two-dimensional NMR spectroscopy.

The solution structure of the phosphocarrier protein, HPr, from Bacillus subtilis has been determined by analysis of two-dimensional (2D) NMR spectra acquired for the unphosphorylated form of the protein. Inverse-detected 2D (1H-15N) heteronuclear multiple quantum correlation nuclear Overhauser effect (HMQC NOESY) and homonuclear Hartmann-Hahn (HOHAHA) spectra utilizing 15N assignments (reported here) as well as previously published 1H assignments were used to identify cross-peaks that are not resolved in 2D homonuclear 1H spectra. Distance constraints derived from NOESY cross-peaks, hydrogen-bonding patterns derived from 1H-2H exchange experiments, and dihedral angle constraints derived from analysis of coupling constants were used for structure calculations using the variable target function algorithm, DIANA. The calculated models were refined by dynamical simulated annealing using the program X-PLOR. The resulting family of structures has a mean backbone rmsd of 0.63 A (N, C alpha, C', O atoms), excluding the segments containing residues 45-59 and 84-88. The structure is comprised of a four-stranded antiparallel beta-sheet with two antiparallel alpha-helices on one side of the sheet. The active-site His 15 residue serves as the N-cap of alpha-helix A, with its N delta 1 atom pointed toward the solvent to accept the phosphoryl group during the phosphotransfer reaction with enzyme I. The existence of a hydrogen bond between the side-chain oxygen atom of Tyr 37 and the amide proton of Ala 56 is suggested, which may account for the observed stabilization of the region that includes the beta-turn comprised of residues 37-40. If the beta alpha beta beta alpha beta (alpha) folding topology of HPr is considered with the peptide chain polarity reversed, the protein fold is identical to that described for another group of beta alpha beta beta alpha beta proteins that include acylphosphatase and the RNA-binding domains of the U1 snRNP A and hnRNP C proteins.     

Solution structure of BmKK4, the first member of subfamily alpha-KTx 17 of scorpion toxins

BmKK4 is a 30 amino acid peptide purified from the venom of the Chinese scorpion Buthus martensi Karsch. It has been classified as the first member of scorpion toxin subfamily alpha-KTx 17. The 3D structure of BmKK4 in solution has been determined by 2D NMR spectroscopy. This toxin adopts a common alpha/beta-motif, but shows a distinctive local conformation. The most novel feature is that the regular arrangements of the side chains of the residues involved in the beta-sheet of BmKK4 are distorted by a classic beta-bulge structure, which involves two residues (Asp18 and Arg19) in the first strand opposite a single residue (Tyr26) in the second strand. The bulge produces two main changes in the structure of the antiparallel beta-sheet: (1) It disrupts the normal alteration of the side chain direction; the side chain of Asp18 turns over to form a salt bridge with that of Arg19. (2) It accentuates the twist of the sheet, and alters the direction of the antiparallel beta-sheet. The unusual structural feature of the toxin is attributed to the shorter peptide segment (Leu15-Arg19) between the third and fourth Cys residues and two unique residues (Asp18 and Arg19) at the position preceding the fourth Cys. In addition, the lower affinity of the peptide for the Kv channel is correlated to the structural features: residue Arg19 instead of a Lys residue at the critical position for binding and the salt bridge formed between residues Arg19 and Asp18.     

Sequence-specific assignment of 1H-NMR resonance and determination of the secondary structure of Jingzhaotoxin-I

Jingzhaotoxin-I （JZTX-I） purified from the venom of the spider Chilobrachys jingzhao is a novel neurotoxin preferentially inhibiting cardiac sodium channel inactivation by binding to receptor site 3.The structure of this toxin in aqueous solution was investigated using 2-D ^1H-NMR techniques. The complete sequence-specific assignments of proton resonance in the ^1H-NMR spectra of JZTX-I were obtained by analyzing a series of 2-D spectra, including DQF-COSY, TOCSY and NOESY spectra, in n20 and D20. All the backbone protons except for Gin4 and more than 95% of the side-chain protons were identified by dαN,dαδ, dβN and dNN connectivities in the NOESY spectrum. These studies provide a basis for the furtherdeter mination of the solution conformation of JZTX-I. Furthermore, the secondary structure of JZTX-I was identified from NMR data. It consists mainly of a short triple-stranded antiparallel β-sheet with Trp7-Cys9, Phe20-Lys23 and Leu28-Trp31. The characteristics of the secondary structure of JZTX-I are similar to those of huwentoxin-I （HWTX-I） and hainantoxin-IV （HNTX-IV）, whose structures in solution havepre viously been reported.     

Solution structure of an analogue of vasoactive intestinal peptide as determined by two-dimensional NMR and circular dichroism spectroscopies and constrained molecular dynamics

Structures have been determined for a potent analogue of vasoactive intestinal peptide (VIP), Ac-[Lys12, Lys14, Nle17, Val26, Thr28]VIP (VIP'), in methanol/water solutions. In CD studies, both VIP and VIP' were helical in methanol/water, with the percentage of alpha-helix increasing with percentage methanol. The pH had little effect on the structure. Complete 1H NMR assignments were made for VIP' in 25% methanol at pH 4 and 6 and in 50% methanol at pH 6, using two-dimensional COSY, NOESY, and relay-COSY experiments. There were no widespread changes in chemical shifts between the samples at pH 4 and 6; however, widespread changes were observed between the samples in 25% and 50% methanol. Complete sets of NOEs were obtained for VIP' in 25% methanol, pH 4, and in 50% methanol, pH 6. These NOEs were converted into distance constraints and applied in molecular dynamics and energy minimization calculations using the program CHARMM. A set of low-energy structures was obtained for VIP' in each solvent system. In 25% methanol, VIP' has two helical segments at residues 9-17 and 23-28. The remainder of the structure is not well determined. In 50% methanol, residues 8-26 form a regular, well-defined alpha-helix and residues 5-8 form a type III beta-turn. The remaining residues are not ordered. These structural assessments agree with the CD data. In the lowest energy structure in 50% methanol, the side chains of Asp3, Phe6, Thr7, and Tyr10 are clustered together--these residues are conserved throughout the family of peptide hormones homologous to VIP.     

Structure of a paralytic peptide from an insect, Manduca sexta.

Paralytic peptide 1 (PP1) from a moth, Manduca sexta, is a 23-residue peptide (Glu-Asn-Phe-Ala-Gly-Gly-Cys-Ala-Thr-Gly-Tyr-Leu-Arg-Thr-Ala-Asp-Gly-Arg -Cys-Lys-Pro-Thr-Phe) that was first found to have paralytic activity when injected into M. sexta larvae. Recent studies demonstrated that PP1 also stimulated the spreading and aggregation of a blood cell type called plasmatocytes and inhibited bleeding from wounds. We determined the solution structure of PP1 by two-dimensional 1H NMR spectroscopy to begin to understand structural-functional relationships of this peptide. PP1 has an ordered structure, which is composed of a short antiparallel beta-sheet at residues Tyr11-Thr14 and Arg18-Pro21, three beta turns at residues Phe3-Gly6, Ala8-Tyr11 and Thr14-Gly17, and a half turn at the carboxyl-terminus (residues Lys20-Phe23). The well-defined secondary and tertiary structure was stabilized by hydrogen bonding and side-chain hydrophobic interactions. In comparison with two related insect peptides, whose structures have been solved recently, the amino-terminal region of PP1 is substantially more ordered. The short antiparallel beta-sheet of PP1 has a folding pattern similar to the carboxyl-terminal subdomain of epidermal growth factor (EGF). Therefore, PP1 may interact with EGF receptor-like molecules to trigger its different biological activities.     

Structure and interactions with RNA of the N-terminal UUAG-specific RNA-binding domain of hnRNP D0

Heterogeneous nuclear ribonucleoprotein (hnRNP) D0 has two ribonucleoprotein (RNP)-type RNA-binding domains (RBDs), each of which can bind solely to the UUAG sequence specifically. The structure of the N-terminal RBD (RBD1) determined by NMR is presented here. It folds into a compact alphabeta structure comprising a four-stranded antiparallel beta-sheet packed against two alpha-helices, which is characteristic of the RNP-type RBDs. Special structural features of RBD1 include N-capping boxes for both alpha-helices, a beta-bulge in the second beta-strand, and an additional short antiparallel beta-sheet coupled with a beta-turn-like structure in a loop. Two hydrogen bonds which restrict the positions of loops were identified. Backbone resonance assignments for RBD1 complexed with r(UUAGGG) revealed that the overall folding is maintained in the complex. The candidate residues involved in the interactions with RNA were identified by chemical shift perturbation analysis. They are located in the central and peripheral regions of the RNA-binding surface composed of the four-stranded beta-sheet, loops, and the C-terminal region. It is suggested that non-specific interactions with RNA are performed by the residues in the central region of the RNA-binding surface, while specific interactions are performed by those in the peripheral regions. It was also found that RBD1 has the ability to inhibit the formation of the quadruplex structure.     

1H NMR sequential resonance assignments, secondary structure, and global fold in solution of the major (trans-Pro43) form of bovine calbindin D9k

A wide range of two-dimensional 1H NMR experiments have been used to completely assign the 500-MHz 1H NMR spectrum of recombinant Ca2+-saturated bovine calbindin D9k (76 amino acids, Mr = 8500). In solution, calbindin D9k exists as an equilibrium mixture of isoforms with trans (75%) and cis (25%) isomers of the peptide bond at Pro43 [Chazin et al. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 2195-2198], which results in two sets of 1H NMR signals from approximately half of the amino acids. The complete 1H NMR assignments for the major, trans-Pro43 isoform are presented here. By use of an integrated strategy for spin system identification, 62 of the 76 spin systems could be assigned to the appropriate residue type. Sequence-specific assignments were then obtained by the standard method. Secondary structure elements were identified on the basis of networks of sequential and medium-range nuclear Overhauser effects (NOEs), 3JHN alpha spin coupling constants, and the location of slowly exchanging amide protons. Four helical segments and a short beta-sheet between the two calcium binding loops are found. These elements of secondary structure and a few additional long-range NOEs provide the global fold. Good agreement is found between the solution and crystal structures of the minor A form of bovine calbindin D9k and between the solution structures of the minor A form of bovine calbindin D9k and intact porcine calbindin D9k.     

High-field NMR and circular dichroism solvent-dependent conformational studies of the bradykinin C-terminal tetrapeptide Ser-Pro-Phe-Arg

The conformational properties of the tetrapeptide Ser1-Pro2-Phe3-Arg4, the C-terminal fragment of the nonapeptide hormone bradykinin, have been studied by circular dichroism and two-dimensional NMR techniques. Measurements of coupling constants, NH temperature dependence rates and nuclear Overhauser effects (performed with rotating frame nuclear Overhauser spectroscopy, ROESY) in H2O and CD3OH/D2O (80/20, v/v) reveal different conformations in the corresponding solvent. In aqueous solution the molecule exists in a random conformation or as an average of several conformations in rapid exchange. In CD3OH/D2O, however, the conformation is well-defined. The backbone of the peptide is extended, and the side-chains of Phe3 and Arg4 exhibit unusual rigidity for a peptide of this size. Evidently, the secondary structure is stabilized by a charge interaction between the guanidino group of Arg4 and the terminal carboxyl group, since experiments at various pH's show clearly that the definition of conformation decreases strongly upon protonation of the carboxyl function. A NH3+(Ser1)-COO-(Arg4) salt bridge, as well as any form of turn stabilized by hydrogen bonds can be ruled out with certainty.     

Solution structure of Escherichia coli Par10: The prototypic member of the Parvulin family of peptidyl-prolyl cis/trans isomerases

E. coli Par10 is a peptidyl-prolyl cis/trans isomerase (PPIase) from Escherichia coli catalyzing the isomerization of Xaa-Pro bonds in oligopeptides with a broad substrate specificity. The structure of E. coli Par10 has been determined by multidimensional solution-state NMR spectroscopy based on 1207 conformational constraints (1067 NOE-derived distances, 42 vicinal coupling-constant restraints, 30 hydrogen-bond restraints, and 68 phi/psi restraints derived from the Chemical Shift Index). Simulated-annealing calculations with the program ARIA and subsequent refinement with XPLOR yielded a set of 18 convergent structures with an average backbone RMSD from mean atomic coordinates of 0.50 A within the well-defined secondary structure elements. E. coli Par10 is the smallest known PPIase so far, with a high catalytic efficiency comparable to that of FKBPs and cyclophilins. The secondary structure of E. coli Par10 consists of four helical regions and a four-stranded antiparallel beta-sheet. The N terminus forms a beta-strand, followed by a large stretch comprising three alpha-helices. A loop region containing a short beta-strand separates these helices from a fourth alpha-helix. The C terminus consists of two more beta-strands completing the four-stranded anti-parallel beta-sheet with strand order 2143. Interestingly, the third beta-strand includes a Gly-Pro cis peptide bond. The curved beta-strand forms a hydrophobic binding pocket together with alpha-helix 4, which also contains a number of highly conserved residues. The three-dimensional structure of Par10 closely resembles that of the human proteins hPin1 and hPar14 and the plant protein Pin1At, belonging to the same family of highly homologous proteins.     

De novo design of a monomeric three-stranded antiparallel beta-sheet

Here we describe the NMR conformational study of a 20-residue linear peptide designed to fold into a monomeric three-stranded antiparallel beta-sheet in aqueous solution. Experimental and statistical data on amino acid beta-turn and beta-sheet propensities, cross-strand side-chain interactions, solubility criteria, and our previous experience with beta-hairpins were considered for a rational selection of the peptide sequence. Sedimentation equilibrium measurements and NMR dilution experiments provide evidence that the peptide is monomeric. Analysis of 1H and 13C-NMR parameters of the peptide, in particular NOEs and chemical shifts, and comparison with data obtained for two 12-residue peptides encompassing the N- and C-segments of the designed sequence indicates that the 20-residue peptide folds into the expected conformation. Assuming a two-state model, the exchange kinetics between the beta-sheet and the unfolded peptide molecules is in a suitable range to estimate the folding rate on the basis of the NMR linewidths of several resonances. The time constant for the coil-beta-sheet transition is of the order of several microseconds in the designed peptide. Future designs based on this peptide system are expected to contribute greatly to our knowledge of the many factors involved in beta-sheet formation and stability.     

Conformational studies of human Des-Trp1,Nle12-minigastrin in water-trifluoroethanol mixtures by 1H NMR and circular dichroism

The 1H NMR spectrum of the title peptide, H-Leu-(Glu)5-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2, in 90% H2O/10% D2O was assigned by two-dimensional methods, and the displacement of the proton resonances upon addition of 2,2,2-trifluoroethanol (TFE) was followed. This permitted the assignment of the spectrum in 90% TFE/10% D2O. While the water conformation of the minigastrin analogue is random, the CD spectrum indicates that an ordered structure is present in TFE. Variable-temperature NMR data in this medium show that six amide protons have low temperature coefficients, two of the five Glu's, Trp, Nle, Asp, and Phe. These results were interpreted in terms of an alpha-helical stretch comprising the Leu and the five Glu residues and a 3(10)-helix initiated by a beta-turn at the sequence -Ala-Tyr-Gly-Trp-. Both CD and NMR data at different solvent compositions show two regions of conformational change, between 20 and 25% water and above 60% water.     

NMR structure of human thymosin alpha-1

800 MHz NMR structure of the 28-residue peptide thymosin alpha-1 in 40% TFE/60% water (v/v) has been determined. Restrained molecular dynamic simulations with an explicit solvent box containing 40% TFE/60% TIP3P water (v/v) were used, in order to get the 3D model of the NMR structure. We found that the peptide adopts a structured conformation having two stable regions: an alpha-helix region from residues 14 to 26 and two double β-turns in the N-terminal twelve residues which form a distorted helical structure.     

Molecular dynamics simulations of peptides containing an unnatural amino acid: dimerization, folding, and protein binding

We have performed molecular dynamics (MD) simulations to study the dimerization, folding, and binding to a protein of peptides containing an unnatural amino acid. NMR studies have shown that the substitution of one residue in a tripeptide beta-strand by the unnatural amino acid Hao (5-HO2CCONH-2-MeO-C6H3-CO-NHNH2) modifies the conformational flexibility of the beta-strand and the hydrogen-bonding properties of its two edges: The number of hydrogen-bond donors and acceptors increases at one edge, whereas at the other, they are sterically hindered. In simulations in chloroform, the Hao-containing peptide 9 (i-PrCO-Phe-Hao-Val-NHBu) forms a beta-sheet-like hydrogen-bonded dimer, in good agreement with the available experimental data. Addition of methanol to the solution induces instability of this beta-sheet, as confirmed by the experiments. MD simulations also reproduce the folding of the synthetic peptide 1a (i-PrCO-Hao-Ut-Phe-Ile-Leu-NHMe) into a beta-hairpin-like structure in chloroform. Finally, the Hao-containing peptide, Ac-Ala-Hao-Ala-NHMe, is shown to form a stable complex with the Ras analogue, Rap1 A, in water at room temperature. Together with the available experimental data, these simulation studies indicate that Hao-containing peptides may serve as inhibitors of beta-sheet interactions between proteins.     

High-resolution mono- and multidimensional magic angle spinning 1H nuclear magnetic resonance of membrane peptides in nondeuterated lipid membranes and H2O.

High-speed (14 kHz) solid-state magic angle spinning (MAS) 1H NMR has been applied to several membrane peptides incorporated into nondeuterated dilauroyl or dimyristoylphosphatidylcholine membranes suspended in H2O. It is shown that solvent suppression methods derived from solution NMR, such as presaturation or jump-return, can be used to reduce water resonance, even at relatively high water content. In addition, regioselective excitation of 1H peptide resonances promotes an efficient suppression of lipid resonances, even in cases where these are initially two orders of magnitude more intense. As a consequence, 1H MAS spectra of the peptide low-field region are obtained without interference from water and lipid signals. These display resonances from amide and other exchangeable 1H as well as from aromatic nonexchangeable 1H. The spectral resolution depends on the specific types of resonance and membrane peptide. For small amphiphilic or hydrophobic oligopeptides, resolution of most individual amide resonance is achieved, whereas for the transmembrane peptide gramicidin A, an unresolved amide spectrum is obtained. Partial resolution of aromatic 1H occurs in all cases. Multidimensional 1H-MAS spectra of membrane peptides can also be obtained by using water suppression and regioselective excitation. For gramicidin A, F2-regioselective 2D nuclear Overhauser effect spectroscopy (NOESY) spectra are dominated by intermolecular through-space connectivities between peptide aromatic or formyl 1H and lipid 1H. These appear to be compatible with the known structure and topography of the gramicidin pore. On the other hand, for the amphiphilic peptide leucine-enkephalin, F2-regioselective NOESY spectra mostly display cross-peaks originating from though-space proximities of amide or aromatic 1H with themselves and with aliphatic 1H. F3-regioselective 3D NOESY-NOESY spectra can be used to obtain through-space correlations within aliphatic 1H. Such intrapeptide proximities should allow determination of the conformation of the peptide in membranes. It is suggested that high-speed MAS multidimensional 1H NMR of peptides in nondeuterated membranes and in H2O can be used for studies of both peptide structure and lipid-peptide interactions.