Polypeptide secondary structure determination by nuclear magnetic resonance observation of short proton-proton distances

[1-7-NαC]-Crocaorb A1 and A2, orbitides from the latex of Croton campanulatus

Two new heptapeptides, [1-7-NαC]-crocaorbs A1 (1) and A2 (2), were isolated from the latex of Croton campanulatus. Their structures were determined using NMR spectroscopic techniques, ESI-HRMS data, Marfey's method, and further refined using molecular dynamics with simulated annealing (MD/SA). Molecular dynamics calculations of peptides 1 and 2 demonstrated greater stability in simulations using a biological solvent compared to those using DMSO. Compound 1, the most abundant peptide in latex, was assessed for NO production, antiplasmodial and cytotoxicity activities. The peptide significantly increased nitric oxide (NO) production at concentrations of 40, 20 or 10 μM (17.932 ± 1.1, 18.270 ± 0.9, 18.499 ± 0.7, respectively). Its antiplasmodial activity exhibited limited efficacy, with only 5% inhibition of Plasmodium falciparum 3D7 growth at a concentration of 50 μM. Also, it exhibited no cytotoxic effects in the J774A.1 murine macrophages cell line. This study represents the first report of a phytochemical investigation of the species C. campanulatus, which showed orbitides with distinctive sequences in contrast to other peptides described for the genus Croton and contributes to the study of structural diversity within this particular class of compounds.

Solution structure and pressure response of thioredoxin-1 of Plasmodium falciparum

We present here the solution structures of the protein thioredoxin-1 from Plasmodium falciparum (PfTrx-1), in its reduced and oxidized forms. They were determined by high-resolution NMR spectroscopy at 293 K on uniformly 13C-, 15N-enriched, matched samples allowing to identification of even small structural differences. PfTrx-1 shows an α/β-fold with a mixed five-stranded β-sheet that is sandwiched between 4 helices in a β1 α1 β2 α2 β3 α3 β4 β5 α4 topology. The redox process of the CGPC motif leads to significant structural changes accompanied by larger chemical shift changes from residue Phe25 to Ile36, Thr70 to Thr74, and Leu88 to Asn91. By high-field high-pressure NMR spectroscopy, rare conformational states can be identified that potentially are functionally important and can be used for targeted drug development. We performed these experiments in the pressure range from 0.1 MPa to 200 MPa. The mean combined, random-coil corrected B1* values of reduced and oxidized thioredoxin are quite similar with -0.145 and -0.114 ppm GPa-1, respectively. The mean combined, random-coil corrected B2* values in the reduced and oxidized form are 0.179 and 0.119 ppm GPa-2, respectively. The mean ratios of the pressure coefficients B2/B1 are -0.484 and -0.831 GPa-1 in the reduced and oxidized form respectively. They differ at some points in the structure after the formation of the disulfide bond between C30 and C33. The thermodynamical description of the pressure dependence of chemical shifts requires the assumption of at least three coexisting conformational states of PfTrx-1. These three conformational states were identified in the reduced as well as in the oxidized form of the protein, therefore, they represent sub-states of the two main oxidation states of PfTrx-1.

Improved methodology for protein NMR structure calculation using hydrogen bond restraints and ANSURR validation: The SH2 domain of SH2B1

Protein structures calculated using NMR data are less accurate and less well-defined than they could be. Here we use the program ANSURR to show that this deficiency is at least in part due to a lack of hydrogen bond restraints. We describe a protocol to introduce hydrogen bond restraints into the structure calculation of the SH2 domain from SH2B1 in a systematic and transparent way and show that the structures generated are more accurate and better defined as a result. We also show that ANSURR can be used as a guide to know when the structure calculation is good enough to stop.

The C-Terminus of Panusin, a Lobster β-Defensin, Is Crucial for Optimal Antimicrobial Activity and Serum Stability

β-defensins are one of the most abundant and studied families of antimicrobial peptides (AMPs). Because of their selective toxicity to bacterial membranes and a broad spectrum of microbicidal action, β-defensins are regarded as potential therapeutic agents. This work focuses on a β-defensin-like AMP from the spiny lobster Panulirus argus (hereafter referred to as panusin or PaD). This AMP is structurally related to mammalian defensins via the presence of an αβ domain stabilized by disulfide bonds. Previous studies of PaD suggest that its C-terminus (Ct_PaD) contains the main structural determinants of antibacterial activity. To confirm this hypothesis, we made synthetic versions of PaD and Ct_PaD to determine the influence of the C-terminus on antimicrobial activity, cytotoxicity, proteolytic stability, and 3D structure. After successful solid-phase synthesis and folding, antibacterial assays of both peptides showed truncated Ct_PaD to be more active than native PaD, confirming the role of the C-terminus in activity and suggesting that cationic residues in that region enhance binding to negatively charged membranes. On the other hand, neither PaD nor Ct_PaD were hemolytic or cytotoxic in human cells. Proteolysis in human serum was also studied, showing high (>24 h) t_1/2 values for PaD and lower but still considerable for Ct_PaD, indicating that the missing native disulfide bond in Ct_PaD alters protease resistance, albeit not decisively. NMR-2D experiments in water agree with the results obtained by circular dichroism (CD), where in SDS micelles, CD showed both peptides adopting an increasingly ordered structure in a hydrophobic environment, in tune with their ability to perturb bacterial membrane systems. In conclusion, while the β-defensin features of PaD are confirmed as advantageous in terms of antimicrobial activity, toxicity, and protease stability, the results of the present work suggest that these same features are preserved, even enhanced, in the structurally simpler Ct_PaD, which must therefore be viewed as a valuable lead for the development of novel anti-infectives.

TapA acts as specific chaperone in TasA filament formation by strand complementation

Studying mechanisms of bacterial biofilm generation is of vital importance to understanding bacterial cell-cell communication, multicellular cohabitation principles, and the higher resilience of microorganisms in a biofilm against antibiotics. Biofilms of the nonpathogenic, gram-positive soil bacterium Bacillus subtilis serve as a model system with biotechnological potential toward plant protection. Its major extracellular matrix protein components are TasA and TapA. The nature of TasA filaments has been of debate, and several forms, amyloidic and non-Thioflavin T-stainable have been observed. Here, we present the three-dimensional structure of TapA and uncover the mechanism of TapA-supported growth of nonamyloidic TasA filaments. By analytical ultracentrifugation and NMR, we demonstrate TapA-dependent acceleration of filament formation from solutions of folded TasA. Solid-state NMR revealed intercalation of the N-terminal TasA peptide segment into subsequent protomers to form a filament composed of β-sandwich subunits. The secondary structure around the intercalated N-terminal strand β0 is conserved between filamentous TasA and the Fim and Pap proteins, which form bacterial type I pili, demonstrating such construction principles in a gram-positive organism. Analogous to the chaperones of the chaperone-usher pathway, the role of TapA is in donating its N terminus to serve for TasA folding into an Ig domain-similar filament structure by donor-strand complementation. According to NMR and since the V-set Ig fold of TapA is already complete, its participation within a filament beyond initiation is unlikely. Intriguingly, the most conserved residues in TasA-like proteins (camelysines) of Bacillaceae are located within the protomer interface.

Examining Topoisomers of a Snake-Venom-Derived Peptide for Improved Antimicrobial and Antitumoral Properties

Ctn[15-34], the C-terminal section of crotalicidin (Ctn), a cathelicidin from a South American pit viper, is an antimicrobial and antitumoral peptide with remarkably longer stability in human serum than the parent Ctn. In this work, a set of topoisomers of both Ctn and Ctn[15-34], including the retro, enantio, and retroenantio versions, were synthesized and tested to investigate the structural requirements for activity. All topoisomers were as active as the cognate sequences against Gram-negative bacteria and tumor cells while slightly more toxic towards normal cells. More importantly, the enhanced serum stability of the D-amino-acid-containing versions suggests that such topoisomers must be preferentially considered as future antimicrobial and anticancer peptide leads.

Helical structure in cyclic peptides: effect of N-methyl amides versus esters

Cyclic peptides with esters but not N-methyl amides are the smallest known alpha helices in water and can enter cells.

Inter-hairpin linker sequences determine the structure of the ββ-solenoid fold: a "bottom-up" study of pneumococcal LytA choline-binding module

The ββ-solenoid structures are part of many proteins involved in the recognition of bacterial cell wall. They are elongated polypeptides consisting of repeated β-hairpins connected by linker sequences and disposed around a superhelical axis stabilised by short-range interactions. Among the most studied ββ-solenoids are those belonging to the family of choline-binding modules (CBMs) from the respiratory pathogen Streptococcus pneumoniae (pneumococcus) and its bacteriophages, and their properties have been employed to develop several biotechnological and biomedical tools. We have carried out a theoretical, spectroscopic and thermodynamic study of the ββ-solenoid structure of the CBM from the pneumococcal LytA autolysin using peptides of increasing length containing 1-3 repeats of this structure. Our results show that hints of native-like tertiary structure are only observed with a minimum of three β-hairpins, corresponding to one turn of the solenoid superhelix, and identify the linker sequences between hairpins as the major directors of the solenoid folding. This study paves the way for the rational structural engineering of ββ-solenoids aimed to find novel applications.

DD04107-Derived neuronal exocytosis inhibitor peptides: Evidences for synaptotagmin-1 as a putative target

The analgesic peptide DD04107 (Pal-EEMQRR-NH₂) and its acetylated analogue inhibit α-calcitonin gene-related peptide (α-CGRP) exocytotic release from primary sensory neurons. Examining the crystal structure of the SNARE-Synaptotagmin-1(Syt1) complex, we hypothesized that these peptides could inhibit neuronal exocytosis by binding to Syt1, hampering at least partially its interaction with the SNARE complex. To address this hypothesis, we first interrogate the role of individual side-chains on the inhibition of α-CGRP release, finding that E1, M3, Q4 and R6 residues were crucial for activity. CD and NMR conformational analysis showed that linear peptides have tendency to adopt α-helical conformations, but the results with cyclic analogues indicated that this secondary structure is not needed for activity. Isothermal titration calorimetry (ITC) measurements demonstrate a direct interaction of some of these peptides with Syt1-C2B domain, but not with Syt7-C2B region, indicating selectivity. As expected for a compound able to inhibit α-CGRP release, cyclic peptide derivative Pal-E-cyclo[EMQK]R-NH₂ showed potent in vivo analgesic activity, in a model of inflammatory pain. Molecular dynamics simulations provided a model consistent with K_D values for the interaction of peptides with Syt1-C2B domain, and with their biological activity. Altogether, these results identify Syt1 as a potential new analgesic target.

NMR Spectroscopy in the Conformational Analysis of Peptides: An Overview

BACKGROUND

NMR spectroscopy is one of the most powerful tools to study the structure and interaction properties of peptides and proteins from a dynamic perspective. Knowing the bioactive conformations of peptides is crucial in the drug discovery field to design more efficient analogue ligands and inhibitors of protein-protein interactions targeting therapeutically relevant systems.

OBJECTIVE

This review provides a toolkit to investigate peptide conformational properties by NMR.

METHODS

Articles cited herein, related to NMR studies of peptides and proteins were mainly searched through PubMed and the web. More recent and old books on NMR spectroscopy written by eminent scientists in the field were consulted as well.

RESULTS

The review is mainly focused on NMR tools to gain the 3D structure of small unlabeled peptides. It is more application-oriented as it is beyond its goal to deliver a profound theoretical background. However, the basic principles of 2D homonuclear and heteronuclear experiments are briefly described. Protocols to obtain isotopically labeled peptides and principal triple resonance experiments needed to study them, are discussed as well.

CONCLUSION

NMR is a leading technique in the study of conformational preferences of small flexible peptides whose structure can be often only described by an ensemble of conformations. Although NMR studies of peptides can be easily and fast performed by canonical protocols established a few decades ago, more recently we have assisted to tremendous improvements of NMR spectroscopy to investigate instead large systems and overcome its molecular weight limit.

Structure of Nanobody Nb23

Background: Nanobodies, or VHHs, are derived from heavy chain-only antibodies (hcAbs) found in camelids. They overcome some of the inherent limitations of monoclonal antibodies (mAbs) and derivatives thereof, due to their smaller molecular size and higher stability, and thus present an alternative to mAbs for therapeutic use. Two nanobodies, Nb23 and Nb24, have been shown to similarly inhibit the self-aggregation of very amyloidogenic variants of β2-microglobulin. Here, the structure of Nb23 was modeled with the Chemical-Shift (CS)-Rosetta server using chemical shift assignments from nuclear magnetic resonance (NMR) spectroscopy experiments, and used as prior knowledge in PONDEROSA restrained modeling based on experimentally assessed internuclear distances. Further validation was comparatively obtained with the results of molecular dynamics trajectories calculated from the resulting best energy-minimized Nb23 conformers. Methods: 2D and 3D NMR spectroscopy experiments were carried out to determine the assignment of the backbone and side chain hydrogen, nitrogen and carbon resonances to extract chemical shifts and interproton separations for restrained modeling. Results: The solution structure of isolated Nb23 nanobody was determined. Conclusions: The structural analysis indicated that isolated Nb23 has a dynamic CDR3 loop distributed over different orientations with respect to Nb24, which could determine differences in target antigen affinity or complex lability.

Swapping the Positions in a Cross-Strand Lateral Ion-Pairing Interaction between Ammonium- and Carboxylate-Containing Residues in a β-Hairpin

Cross-strand lateral ion-pairing interactions are important for antiparallel β-sheet stability. Statistical studies suggested that swapping the position of cross-strand lateral residues should not significantly affect the interaction. Herein, we swapped the position of ammonium- and carboxylate-containing residues with different side-chain lengths in a cross-strand lateral ion-pairing interaction in a β-hairpin. The peptides were analyzed by 2D-NMR. The fraction folded population and folding free energy were derived from the chemical shift data. The ion-pairing interaction energy was derived using double mutant cycle analysis. The general trends for the fraction folded population and interaction energetics remained similar upon swapping the position of the interacting charged residues. The most stabilizing cross-strand interactions were between short residues, similar to the unswapped study. However, the fraction folded populations for most of the swapped peptides were higher compared to the corresponding unswapped peptides. Furthermore, subtle differences in the ion-pairing interaction energy upon swapping were observed, most likely due to the “unleveled” relative positioning of the interacting residues created by the inherent right-handed twist of the structure. These results should be useful for developing functional peptides that rely on lateral ion-pairing interactions across antiparallel β-strands.

Solid-phase synthesis and bioactivity evaluation of cherimolacyclopeptide E

Cherimolacylopeptide E (1) is a cyclic hexapeptide isolated from the seeds of Annona cherimola. Peptide 1 reportedly exhibits potent cytotoxicity against KB cells (IC₅₀ 0.017 μM). To confirm the structure and bioactivity of 1, we conducted a total synthesis of its proposed structure. The synthesis was accomplished via solid-phase peptide elongation and macrocyclization by employing Fmoc/OAll-protected amino acids on 2-Cl-trityl resin. NMR analysis revealed that synthetic 1 exists in two conformations in pyridine-d₅ . As the spectroscopic data of the major conformer of synthetic 1 were consistent with those of natural 1, the structure of cherimolacyclopeptide E was confirmed to be 1. However, our synthetic 1 exhibited low cytotoxicity against KB cells (IC₅₀ > 100 μM). In contrast to previously-reported findings, our synthetic 1 exhibited little antibacterial activity against Escherichia coli.

REDCRAFT: A computational platform using residual dipolar coupling NMR data for determining structures of perdeuterated proteins in solution

Nuclear Magnetic Resonance (NMR) spectroscopy is one of the three primary experimental means of characterizing macromolecular structures, including protein structures. Structure determination by solution NMR spectroscopy has traditionally relied heavily on distance restraints derived from nuclear Overhauser effect (NOE) measurements. While structure determination of proteins from NOE-based restraints is well understood and broadly used, structure determination from Residual Dipolar Couplings (RDCs) is relatively less well developed. Here, we describe the new features of the protein structure modeling program REDCRAFT and focus on the new Adaptive Decimation (AD) feature. The AD plays a critical role in improving the robustness of REDCRAFT to missing or noisy data, while allowing structure determination of larger proteins from less data. In this report we demonstrate the successful application of REDCRAFT in structure determination of proteins ranging in size from 50 to 145 residues using experimentally collected data, and of larger proteins (145 to 573 residues) using simulated RDC data. In both cases, REDCRAFT uses only RDC data that can be collected from perdeuterated proteins. Finally, we compare the accuracy of structure determination from RDCs alone with traditional NOE-based methods for the structurally novel PF.2048.1 protein. The RDC-based structure of PF.2048.1 exhibited 1.0 Å BB-RMSD with respect to a high-quality NOE-based structure. Although optimal strategies would include using RDC data together with chemical shift, NOE, and other NMR data, these studies provide proof-of-principle for robust structure determination of largely-perdeuterated proteins from RDC data alone using REDCRAFT.

Residual Dipolar Couplings have the potential to improve the accuracy and reduce the time needed to characterize protein structures. In addition, RDC data have been demonstrated to concurrently elucidate structure of proteins, provide assignment of resonances, and characterize the internal dynamics of proteins. Given all the advantages associated with the study of proteins from RDC data, based on the statistics provided by the Protein Databank (PDB), surprisingly only 124 proteins (out of nearly 150,000 proteins) have utilized RDCs as part of their structure determination. Even a smaller subset of these proteins (approximately 7) have utilized RDCs as the primary source of data for structure determination. One key factor in the use of RDCs is the challenging computational and analytical aspects of this source of data. In this report, we demonstrate the success of the REDCRAFT software package in structure determination of proteins using RDC data that can be collected from small and large proteins in a routine fashion. REDCRAFT accomplishes the challenging task of structure determination from RDCs by introducing a unique search and optimization technique that is both robust and computationally tractable. Structure determination from routinely collectable RDC data using REDCRAFT can complement existing methods to provide faster and more accurate studies of larger and more complex protein structures by NMR spectroscopy in solution state.

Dynamic Stereoselection of Peptide Helicates and Their Selective Labeling of DNA Replication Foci in Cells*

Although largely overlooked in peptide engineering, coordination chemistry offers a new set of interactions that opens unexplored design opportunities for developing complex molecular structures. In this context, we report new artificial peptide ligands that fold into chiral helicates in the presence of labile metal ions such as Fe^II and Co^II . Heterochiral β-turn-promoting sequences encode the stereoselective folding of the peptide ligands and define the physicochemical properties of their corresponding metal complexes. Circular dichroism and NMR spectroscopy in combination with computational methods allowed us to identify and determine the structure of two isochiral ΛΛ-helicates, folded as topological isomers. Finally, in addition to the in-vitro characterization of their selective binding to DNA three-way junctions, cell-microscopy experiments demonstrated that a rhodamine-labeled Fe^II helicate was internalized and selectively stains DNA replication factories in functional cells.

Structural Insights into β-arrestin/CB1 Receptor Interaction: NMR and CD Studies on Model Peptides

Activation of the cannabinoid CB1 receptor induces different cellular signaling cascades through coupling to different effector proteins (G-proteins and β-arrestins), triggering numerous therapeutic effects. Conformational changes and rearrangements at the intracellular domain of this GPCR receptor that accompany ligand binding dictate the signaling pathways. The GPCR-binding interface for G proteins has been extensively studied, whereas β-arrestin/GPCR complexes are still poorly understood. To gain knowledge in this direction, we designed peptides that mimic the motifs involved in the putative interacting region: β-arrestin1 finger loop and the transmembrane helix 7-helix 8 (TMH7-H8) elbow located at the intracellular side of the CB1 receptor. According to circular dichroism and NMR data, these peptides form a native-like, helical conformation and interact with each other in aqueous solution, in the presence of trifluoroethanol, and using zwitterionic detergent micelles as membrane mimics. These results increase our understanding of the binding mode of β-arrestin and CB1 receptor and validate minimalist approaches to structurally comprehend complex protein systems.

Complete sequential assignment and secondary structure prediction of the cannulae forming protein CanA from the hyperthermophilic archaeon Pyrodictium abyssi

CanA from Pyrodictium abyssi forms a heat-resistant organic hollow-fiber network together with CanB and CanC. An N-terminally truncated construct of CanA (K1-CanA) gave NMR spectra of good quality that could be assigned by three-dimensional NMR methods on 15N and 13C-15N enriched protein. We assigned the chemical shifts of 96% of all backbone 1HN atoms, 98% of all backbone 15N atoms, 100% of all 13Cα atoms, 100% of all 1Hα atoms, 90% of all 13C' atoms, and 100% of the 13Cβ atoms. Two short helices and 10 β-strands are estimated from an analysis of the chemical shifts leading to a secondary structure content of K1-CanA of 6% helices, 44% β-pleated sheets, and 50% coils.

Pro-islet amyloid polypeptide in micelles contains a helical prohormone segment

Pro-islet amyloid polypeptide (proIAPP) is the prohormone precursor molecule to IAPP, also known as amylin. IAPP is a calcitonin family peptide hormone that is cosecreted with insulin, and largely responsible for hunger satiation and metabolic homeostasis. Amyloid plaques containing mixtures of mature IAPP and misprocessed proIAPP deposit on, and destroy pancreatic β-cell membranes, and they are recognized as a clinical hallmark of type 2 diabetes mellitus. In order to better understand the interaction with cellular membranes, we solved the solution NMR structure of proIAPP bound to dodecylphosphocholine micelles at pH 4.5. We show that proIAPP is a dynamic molecule with four α-helices. The first two helices are contained within the mature IAPP sequence, while the second two helices are part of the C-terminal prohormone segment (Cpro). We mapped the membrane topology of the amphipathic helices by paramagnetic relaxation enhancement, and we used CD and diffusion-ordered spectroscopy to identify environmental factors that impact proIAPP membrane affinity. We discuss how our structural results relate to prohormone processing based on the varied pH environments and lipid compositions of organelle membranes within the regulated secretory pathway, and the likelihood of Cpro survival for cosecretion with IAPP. DATABASE: The assigned resonances have been deposited in the Biological Magnetic Resonance Bank (BMRB) with accession numbers 50007 and 50019 for proIAPP and Cpro, respectively. The lowest energy structures have been deposited in the Protein Data Bank (PDB) with access codes 6UCJ and 6UCK.

Controlling the dynamics of the Nek2 leucine zipper by engineering of "kinetic" disulphide bonds

Nek2 is a dimeric serine/ threonine protein kinase that belongs to the family of NIMA-related kinases (Neks). Its N-terminal catalytic domain and its C-terminal regulatory region are bridged by a leucine zipper, which plays an important role in the activation of Nek2's catalytic activity. Unusual conformational dynamics on the intermediary/slow timescale has thwarted all attempts so far to determine the structure of the Nek2 leucine zipper by means of X-ray crystallography and Nuclear Magnetic Resonance (NMR). Disulfide engineering, the strategic placement of non-native disulfide bonds into flexible regions flanking the coiled coil, was used to modulate the conformational exchange dynamics of this important dimerization domain. The resulting reduction in exchange rate leads to substantial improvements of important features in NMR spectra, such as line width, coherence transfer leakage and relaxation. These effects were comprehensively analyzed for the wild type protein, two single disulfide bond-bearing mutants and another double disulfide bonds-carrying mutant. Furthermore, exchange kinetics were measured across a wide temperature range, allowing for a detailed analysis of activation energy (ΔG‡) and maximal rate constant (k'ex). For one mutant carrying a disulfide bond at its C-terminus, a full backbone NMR assignment could be obtained for both conformers, demonstrating the benefits of the disulfide engineering. Our study demonstrates the first successful application of 'kinetic' disulfide bonds for the purpose of controlling the adverse effects of protein dynamics. Firstly, this provides a promising, robust platform for the full structural and functional investigation of the Nek2 leucine zipper in the future. Secondly, this work broadens the toolbox of protein engineering by disulfide bonds through the addition of a kinetic option in addition to the well-established thermodynamic uses of disulfide bonds.

CB1 cannabinoid receptor-phosphorylated fourth intracellular loop structure-function relationships

A peptide comprising the juxtamembrane C-terminal intracellular loop 4 (IL4) of the CB₁ cannabinoid receptor possesses three Serine residues (Ser402, Ser411 and Ser415). Here we report the effect of Ser phosphorylation on the CB₁ IL4 peptide conformation and cellular signaling functions using nuclear magnetic resonance spectroscopy, circular dichroism, G protein activation and cAMP production. Circular dichroism studies indicated that phosphorylation at various Ser residues induced helical structure in different environments. NMR data indicates that helical content varies in the order of IL4pSer411 > IL4pSer415 > IL4 > IL4pSer402. The efficacy of phosphorylated IL4 peptides in activating Go and Gi3 ([³⁵S]GTPγS binding) and inhibiting cAMP accumulation in N18TG2 cells were correlated with helicity changes. Treatment of cells with bradykinin, which activates PKC, augmented CB₁-mediated inhibition of cAMP accumulation, and this was reversed by a PKC inhibitor, suggesting that phosphorylation of serine might be a physiologically relevant modification in vivo. We conclude that phosphorylation-dependent alterations of helicity of CB₁ IL4 peptides can increase efficacy of G protein signaling.

A Potent Conformation-Constrained Synthetic Peptide Mimic of a Homeodomain Selectively Regulates Target Genes in Cells

DNA, as a target for therapeutic intervention, remains largely unexplored. DLX-4, a homeodomain containing transcription factor, and its spliced isoforms play crucial roles in many aspects of cellular biochemistry and important roles in many diseases. A smaller peptide mimicking the homeodomain of the transcription factor DLX-4 was designed and synthesized by suitable conjoining of its modified DNA-binding elements. The peptide binds to DLX-4 target sites on the regulatory region of the globin gene cluster with native-like affinity and specificity in vitro. When conjugated to cell penetrating and nuclear localization sequences, it upregulated some of the genes repressed by DLX-4 or its isoforms, such as β- and γ-globin genes in erythropoietin-induced differentiating CD34⁺ human hematopoietic stem/progenitor cells with high specificity by competing with the respective binding sites. Engineered peptides mimicking DNA-binding domains of transcription factors offer the potential for creating synthetic molecules for directly targeting DNA sites with high specificity.

Conformational Properties of a Peptidic Catalyst: Insights from NMR Spectroscopic Studies

Peptides have become valuable as catalysts for a variety of different reactions, but little is known about the conformational properties of peptidic catalysts. We investigated the conformation of the peptide H-dPro-Pro-Glu-NH₂, a highly reactive and stereoselective catalyst for conjugate addition reactions, and the corresponding enamine intermediate in solution by NMR spectroscopy and computational methods. The combination of nuclear Overhauser effects (NOEs), residual dipolar couplings (RDCs), J-couplings, and temperature coefficients revealed that the tripeptide adopts a single predominant conformation in its ground state. The structure is a type I β-turn, which gains stabilization from three hydrogen bonds that are cooperatively formed between all functional groups (secondary amine, carboxylic acid, amides) within the tripeptide. In contrast, the conformation of the enamine intermediate is significantly more flexible. The conformational ensemble of the enamine is still dominated by the β-turn, but the backbone and the side chain of the glutamic acid residue are more dynamic. The key to the switch between rigidity and flexibility of the peptidic catalyst is the CO₂H group in the side chain of the glutamic acid residue, which acts as a lid that can open and close. As a result, the peptidic catalyst is able to adapt to the structural requirements of the intermediates and transition states of the catalytic cycle. These insights might explain the robustness and high reactivity of the peptidic catalyst, which exceeds that of other secondary amine-based organocatalysts. The data suggest that a balance between rigidity and flexibility, which is reminiscent of the dynamic nature of enzymes, is beneficial for peptidic catalysts and other synthetic catalysts.

Solution conformation of a cohesin module and its scaffoldin linker from a prototypical cellulosome

Bacterial cellulases are drawing increased attention as a means to obtain plentiful chemical feedstocks and fuels from renewable lignocellulosic biomass sources. Certain bacteria deploy a large extracellular multi-protein complex, called the cellulosome, to degrade cellulose. Scaffoldin, a key non-catalytic cellulosome component, is a large protein containing a cellulose-specific carbohydrate-binding module and several cohesin modules which bind and organize the hydrolytic enzymes. Despite the importance of the structure and protein/protein interactions of the cohesin module in the cellulosome, its structure in solution has remained unknown to date. Here, we report the backbone 1H, 13C and 15N NMR assignments of the Cohesin module 5 from the highly stable and active cellulosome from Clostridium thermocellum. These data reveal that this module adopts a tightly packed, well folded and rigid structure in solution. Furthermore, since in scaffoldin, the cohesin modules are connected by linkers we have also characterized the conformation of a representative linker segment using NMR spectroscopy. Analysis of its chemical shift values revealed that this linker is rather stiff and tends to adopt extended conformations. This suggests that the scaffoldin linkers act to minimize interactions between cohesin modules. These results pave the way towards solution studies on cohesin/dockerin's fascinating dual-binding mode.

Roles of Amphipathicity and Hydrophobicity in the Micelle-Driven Structural Switch of a 14-mer Peptide Core from a Choline-Binding Repeat

Choline-binding repeats (CBRs) are ubiquitous sequences with a β-hairpin core that are found in the surface proteins of several microorganisms such as S. pneumoniae (pneumococcus). Previous studies on a 14-mer CBR sequence derived from the pneumoccal LytA autolysin (LytA_239-252 peptide) have demonstrated a switch behaviour for this peptide, so that it acquires a stable, native-like β-hairpin conformation in aqueous solution but is reversibly transformed into an amphipathic α-helix in the presence of detergent micelles. With the aim of understanding the factors responsible for this unusual β-hairpin to α-helix transition, and to specifically assess the role of peptide hydrophobicity and helical amphipathicity in the process, we designed a series of LytA_239-252 variants affecting these two parameters and studied their interaction with dodecylphosphocholine (DPC) micelles by solution NMR, circular dichroism and fluorescence spectroscopies. Our results indicate that stabilising cross-strand interactions become essential for β-hairpin stability in the absence of optimal turn sequences. Moreover, both amphipathicity and hydrophobicity display comparable importance for helix stabilisation of CBR-derived peptides in micelles, indicating that these sequences represent a novel class of micelle/membrane-interacting peptides.

Structure-Related Roles for the Conservation of the HIV-1 Fusion Peptide Sequence Revealed by Nuclear Magnetic Resonance

Despite extensive characterization of the human immunodeficiency virus type 1 (HIV-1) hydrophobic fusion peptide (FP), the structure-function relationships underlying its extraordinary degree of conservation remain poorly understood. Specifically, the fact that the tandem repeat of the FLGFLG tripeptide is absolutely conserved suggests that high hydrophobicity may not suffice to unleash FP function. Here, we have compared the nuclear magnetic resonance (NMR) structures adopted in nonpolar media by two FP surrogates, wtFP-tag and scrFP-tag, which had equal hydrophobicity but contained wild-type and scrambled core sequences LFLGFLG and FGLLGFL, respectively. In addition, these peptides were tagged at their C-termini with an epitope sequence that folded independently, thereby allowing Western blot detection without interfering with FP structure. We observed similar α-helical FP conformations for both specimens dissolved in the low-polarity medium 25% (v/v) 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), but important differences in contact with micelles of the membrane mimetic dodecylphosphocholine (DPC). Thus, whereas wtFP-tag preserved a helix displaying a Gly-rich ridge, the scrambled sequence lost in great part the helical structure upon being solubilized in DPC. Western blot analyses further revealed the capacity of wtFP-tag to assemble trimers in membranes, whereas membrane oligomers were not observed in the case of the scrFP-tag sequence. We conclude that, beyond hydrophobicity, preserving sequence order is an important feature for defining the secondary structures and oligomeric states adopted by the HIV FP in membranes.

NMR Insights into the Structure-Function Relationships in the Binding of Melanocortin Analogues to the MC1R Receptor

Linear and cyclic analogues of the α-melanocyte stimulating hormone (α-MSH) targeting the human melanocortin receptor 1 (MC1R) are of pharmacological interest for detecting and treating melanoma. The central sequence of α-MSH (His-Phe-Arg-Trp) has been identified as being essential for receptor binding. To deepen current knowledge on the molecular basis for α-MSH bioactivity, we aimed to understand the effect of cycle size on receptor binding. To that end, we synthesised two macrocyclic isomeric α-MSH analogues, c[NH-NO₂-C₆H₃-CO-His-DPhe-Arg-Trp-Lys]-Lys-NH₂ (CycN-K6) and c[NH-NO₂-C₆H₃-CO-His-DPhe-Arg-Trp-Lys-Lys]-NH₂ (CycN-K7). Their affinities to MC1R receptor were determined by competitive binding assays, and their structures were analysed by ¹H and ¹³C NMR. These results were compared to those of the previously reported analogue c[S-NO₂-C₆H₃-CO-His-DPhe-Arg-Trp-Cys]-Lys-NH₂ (CycS-C6). The MC1R binding affinity of the 22-membered macrocyclic peptide CycN-K6 (IC₅₀ = 155 ± 16 nM) is higher than that found for the 25-membered macrocyclic analogue CycN-K7 (IC₅₀ = 495 ± 101 nM), which, in turn, is higher than that observed for the 19-membered cyclic analogue CycS-C6 (IC₅₀ = 1770 ± 480 nM). NMR structural study indicated that macrocycle size leads to changes in the relative dispositions of the side chains, particularly in the packing of the Arg side chain relative to the aromatic rings. In contrast to the other analogues, the 22-membered cycle’s side chains are favorably positioned for receptor interaction.

Helical-Peptide-Catalyzed Enantioselective Michael Addition Reactions and Their Mechanistic Insights

Helical peptide foldamer catalyzed Michael addition reactions of nitroalkane or dialkyl malonate to α,β-unsaturated ketones are reported along with the mechanistic considerations of the enantio-induction. A wide variety of α,β-unsaturated ketones, including β-aryl, β-alkyl enones, and cyclic enones, were found to be catalyzed by the helical peptide to give Michael adducts with high enantioselectivities (up to 99%). On the basis of X-ray crystallographic analysis and depsipeptide study, the amide protons, N(2)-H and N(3)-H, at the N terminus in the α-helical peptide catalyst were crucial for activating Michael donors, while the N-terminal primary amine activated Michael acceptors through the formation of iminium ion intermediates.

PSCD Domains of Pleuralin-1 from the Diatom Cylindrotheca fusiformis: NMR Structures and Interactions with Other Biosilica-Associated Proteins

Diatoms are eukaryotic unicellular algae characterized by silica cell walls and associated with three unique protein families, the pleuralins, frustulins, and silaffins. The NMR structure of the PSCD4 domain of pleuralin-1 from Cylindrotheca fusiformis contains only three short helical elements and is stabilized by five unique disulfide bridges. PSCD4 contains two binding sites for Ca(2+) ions with millimolar affinity. NMR-based interaction studies show an interaction of the domain with native silaffin-1A as well as with α-frustulins. The interaction sites of the two proteins mapped on the PSCD4 structure are contiguous and show only a small overlap. A plausible functional role of pleuralin could be to bind simultaneously silaffin-1A located inside the cell wall and α-frustulin coating the cell wall, thus connecting the interfaces between hypotheca and epitheca at the girdle bands. Restrained molecular dynamics calculations suggest a bead-chain-like structure of the central part of pleuralin-1.

An In-tether Chiral Center Modulates the Helicity, Cell Permeability, and Target Binding Affinity of a Peptide

The addition of a precisely positioned chiral center in the tether of a constrained peptide is reported, yielding two separable peptide diastereomers with significantly different helicity, as supported by circular dichroism (CD) and NMR spectroscopy. Single crystal X-ray diffraction analysis suggests that the absolute configuration of the in-tether chiral center in helical form is R, which is in agreement with theoretical simulations. The relationship between the secondary structure of the short peptides and their biochemical/biophysical properties remains elusive, largely because of the lack of proper controls. The present strategy provides the only method for investigating the influence of solely conformational differences upon the biochemical/biophysical properties of peptides. The significant differences in permeability and target binding affinity between the peptide diastereomers demonstrate the importance of helical conformation.

Biochemical and biophysical combined study of bicarinalin, an ant venom antimicrobial peptide

We have recently characterized bicarinalin as the most abundant peptide from the venom of the ant Tetramorium bicarinatum. This antimicrobial peptide is active against Staphylococcus and Enterobacteriaceae. To further investigate the antimicrobial properties of this cationic and cysteine-free peptide, we have studied its antibacterial, antifungal and antiparasitic activities on a large array of microorganisms. Bicarinalin was active against fifteen microorganisms with minimal inhibitory concentrations ranging from 2 and 25μmolL(-1). Cronobacter sakazakii, Salmonella enterica, Candida albicans, Aspergilus niger and Saccharomyces cerevisiae were particularly susceptible to this novel antimicrobial peptide. Resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and C. albicans were as susceptible as the canonical strains. Interestingly, bicarinalin was also active against the parasite Leishmania infantum with a minimal inhibitory concentrations of 2μmolL(-1). The bicarinalin pre-propeptide cDNA sequence has been determined using a combination of degenerated primers with RACE PCR strategy. Interestingly, the N-terminal domain of bicarinalin pre-propeptide exhibited sequence similarity with the pilosulin antimicrobial peptide family previously described in the Myrmecia venoms. Moreover, using SYTOX green uptake assay, we showed that, for all the tested microorganisms, bicarinalin acted through a membrane permeabilization mechanism. Two dimensional-NMR experiments showed that bicarinalin displayed a 10 residue-long α-helical structure flanked by two N- and C-terminal disordered regions. This partially amphipathic helix may explain the membrane permeabilization mechanism of bicarinalin observed in this study. Finally, therapeutic value of bicarinalin was highlighted by its low cytotoxicity against human lymphocytes at bactericidal concentrations and its long half-life in human serum which was around 15h.

The application of DOSY NMR and molecular dynamics simulations to explore the mechanism(s) of micelle binding of antimicrobial peptides containing unnatural amino acids

Anionic and zwitterionic micelles are often used as simple models for the lipids found in bacterial and mammalian cell membranes to investigate antimicrobial peptide-lipid interactions. In our laboratory we have employed a variety of 1D, 2D, and diffusion ordered (DOSY) NMR experiments to investigate the interactions of antimicrobial peptides containing unnatural amino acids with SDS and DPC micelles. Complete assignment of the proton spectra of these peptides is prohibited by the incorporation of a high percentage of unnatural amino acids which don't contain amide protons into the backbone. However preliminary assignment of the TOCSY spectra of compound 23 in the presence of both micelles indicated multiple conformers are present as a result of binding to these micelles. Chemical Shift Indexing agreed with previously collected CD spectra that indicated on binding to SDS micelles compound 23 adopts a mixture of α-helical structures and on binding to DPC micelles this peptide adopts a mixture of helical and β-turn/sheet like structures. DOSY NMR experiments also indicated that the total positive charge and the relative placement of that charge at the N-terminus or C-terminus are important in determining the mole fraction of the peptide that will bind to the different micelles. DOSY and (1) H-NMR experiments indicated that the length of Spacer #1 plays a major role in defining the binding conformation of these analogs with SDS micelles. Results obtained from molecular simulations studies of the binding of compounds 23 and 36 with SDS micelles were consistent with the observed NMR results.

1H, 15N and 13C resonance assignments of light organ-associated fatty acid-binding protein of Taiwanese fireflies

Fatty acid-binding proteins (FABPs) are a family of proteins that modulate the transfer of various fatty acids in the cytosol and constitute a significant portion in many energy-consuming cells. The ligand binding properties and specific functions of a particular type of FABP seem to be diverse and depend on the respective binding cavity as well as the cell type from which this protein is derived. Previously, a novel FABP (lcFABP; lc: Luciola cerata) was identified in the light organ of Taiwanese fireflies. The lcFABP was proved to possess fatty acids binding capabilities, especially for fatty acids of length C14-C18. However, the structural details are unknown, and the structure-function relationship has remained to be further investigated. In this study, we finished the (1)H, (15)N and (13)C chemical shift assignments of (15)N/(13)C-enriched lcFABP by solution NMR spectroscopy. In addition, the secondary structure distribution was revealed based on the backbone N, H, Cα, Hα, C and side chain Cβ assignments. These results can provide the basis for further structural exploration of lcFABP.

Structure-Correlation NMR Spectroscopy for Macromolecules Using Repeated Bidirectional Photoisomerization of Azobenzene

Control over macromolecular structure offers bright potentials for manipulation of macromolecular functions. We here present structure-correlation NMR spectroscopy to analyze the correlation between polymorphic macromolecular structures driven by photoisomerization of azobenzene. The structural conversion of azobenzene was induced within the mixing time of a NOESY experiment using a colored light source, and the reverse structural conversion was induced during the relaxation delay using a light source of another color. The correlation spectrum between trans- and cis-azobenzene was then obtained. To maximize the efficiency of the bidirectional photoisomerization of azobenzene-containing macromolecules, we developed a novel light-irradiation NMR sample tube and method for irradiating target molecules in an NMR radio frequency (rf) coil. When this sample tube was used for photoisomerization of an azobenzene derivative at a concentration of 0.2 mM, data collection with reasonable sensitivity applicable to macromolecules was achieved. We performed isomerization of an azobenzene-cross-linked peptide within the mixing time of a NOESY experiment that produced cross-peaks between helix and random-coil forms of the peptide. Thus, these results indicate that macromolecular structure manipulation can be incorporated into an NMR pulse sequence using an azobenzene derivative and irradiation with light of two types of wavelengths, providing a new method for structural analysis of metastable states of macromolecules.

Structural Dissection of Crotalicidin, a Rattlesnake Venom Cathelicidin, Retrieves a Fragment with Antimicrobial and Antitumor Activity

In silico dissection of crotalicidin (Ctn), a cathelicidin from a South American pit viper, yielded fragments Ctn[1-14] and Ctn[15-34], which were tested to ascertain to what extent they reproduced the structure and activity of the parent peptide. NMR data showing Ctn to be α-helical at the N-terminus and unstructured at the C-terminus were matched by similar data from the fragments. The peptides were tested against Gram-positive and -negative bacteria and for toxicity against both tumor and healthy cells. Despite its amphipathic α-helical structure, Ctn[1-14] was totally inert toward bacteria or eukaryotic cells. In contrast, unstructured Ctn[15-34] replicated the activity of parent Ctn against Gram-negative bacteria and tumor cells while being significantly less toxic toward eukaryotic cells. This selectivity for bacteria and tumor cells, plus a stability to serum well above that of Ctn, portrays Ctn[15-34] as an appealing candidate for further development as an anti-infective or antitumor lead.

Micelle-Triggered β-Hairpin to α-Helix Transition in a 14-Residue Peptide from a Choline-Binding Repeat of the Pneumococcal Autolysin LytA

Choline-binding modules (CBMs) have a ββ-solenoid structure composed of choline-binding repeats (CBR), which consist of a β-hairpin followed by a short linker. To find minimal peptides that are able to maintain the CBR native structure and to evaluate their remaining choline-binding ability, we have analysed the third β-hairpin of the CBM from the pneumococcal LytA autolysin. Circular dichroism and NMR data reveal that this peptide forms a highly stable native-like β-hairpin both in aqueous solution and in the presence of trifluoroethanol, but, strikingly, the peptide structure is a stable amphipathic α-helix in both zwitterionic (dodecylphosphocholine) and anionic (sodium dodecylsulfate) detergent micelles, as well as in small unilamellar vesicles. This β-hairpin to α-helix conversion is reversible. Given that the β-hairpin and α-helix differ greatly in the distribution of hydrophobic and hydrophilic side chains, we propose that the amphipathicity is a requirement for a peptide structure to interact and to be stable in micelles or lipid vesicles. To our knowledge, this "chameleonic" behaviour is the only described case of a micelle-induced structural transition between two ordered peptide structures.

The Atomic Structure of the HIV-1 gp41 Transmembrane Domain and Its Connection to the Immunogenic Membrane-proximal External Region

The membrane-proximal external region (MPER) C-terminal segment and the transmembrane domain (TMD) of gp41 are involved in HIV-1 envelope glycoprotein-mediated fusion and modulation of immune responses during viral infection. However, the atomic structure of this functional region remains unsolved. Here, based on the high resolution NMR data obtained for peptides spanning the C-terminal segment of MPER and the TMD, we report two main findings: (i) the conformational variability of the TMD helix at a membrane-buried position; and (ii) the existence of an uninterrupted α-helix spanning MPER and the N-terminal region of the TMD. Thus, our structural data provide evidence for the bipartite organization of TMD predicted by previous molecular dynamics simulations and functional studies, but they do not support the breaking of the helix at Lys-683, as was suggested by some models to mark the initiation of the TMD anchor. Antibody binding energetics examined with isothermal titration calorimetry and humoral responses elicited in rabbits by peptide-based vaccines further support the relevance of a continuous MPER-TMD helix for immune recognition. We conclude that the transmembrane anchor of HIV-1 envelope is composed of two distinct subdomains: 1) an immunogenic helix at the N terminus also involved in promoting membrane fusion; and 2) an immunosuppressive helix at the C terminus, which might also contribute to the late stages of the fusion process. The unprecedented high resolution structural data reported here may guide future vaccine and inhibitor developments.

Conformations of a model cyclic hexapeptide, CYIQNC: (1)H-NMR and molecular dynamics studies

Solution conformation of the cyclic hexapeptide sequence, [cyclo-S-Cys-Tyr-Ile-Gln-Asn-Cys-S] (CYIQNC) - a disulfide-linked fragment of a neurohypophyseal peptide hormone oxytocin (OT) - has been investigated by high-field one-dimensional (1D) and two-dimensional (2D) NMR spectroscopic methods and compared with the results obtained from computer simulation studies. (1)H-NMR results based on temperature dependence of amide proton chemical shifts and nuclear Overhauser effect indicate that peptide in solution populates different conformations, characterized by two fused β-turns. The segment Ile(3)-Gln(4)-Asn(5)-Cys(6) yields a preferred type-III β-turn at residues 4, 5 (HB, 3HN → 6CO), while the segment Cys(6), Cys(1)-Tyr(2)-Ile(3) exhibits inherently weaker, flexible β-turn either of type I/II'/III/half-turn at residues 1, 2 (HB, 6HN → 3CO). The computer simulation studies using a mixed protocol of distance geometry-simulated annealing followed by constrained minimization, restrained molecular dynamics, and energy minimization showed the possibility of existence of additional conformations with the hydrogen bonds, (a) 5HN → 3CO and (b) 2HN → 6CO. These results, therefore, indicate that the additional conformations obtained from both NMR and simulation studies can also be possible to the peptide. These additional conformations might have very small population in the solution and did not show their signatures in these conditions. These findings will be helpful in designing more analogs with modifications in the cyclic moiety of OT.

Conformation of dehydropentapeptides containing four achiral amino acid residues - controlling the role of L-valine

Structural studies of pentapeptides containing an achiral block, built from two dehydroamino acid residues (Δ^ZPhe and ΔAla) and two glycines, as well as one chiral L-Val residue were performed using NMR spectroscopy. The key role of the L-Val residue in the generation of the secondary structure of peptides is discussed. The obtained results suggest that the strongest influence on the conformation of peptides arises from a valine residue inserted at the C-terminal position. The most ordered conformation was found for peptide Boc-Gly-ΔAla-Gly-Δ^ZPhe-Val-OMe (3), which adopts a right-handed helical conformation.

Structure and immunogenicity of a peptide vaccine, including the complete HIV-1 gp41 2F5 epitope: implications for antibody recognition mechanism and immunogen design

The membrane-proximal external region (MPER) of gp41 harbors the epitope recognized by the broadly neutralizing anti-HIV 2F5 antibody, a research focus in HIV-1 vaccine development. In this work, we analyze the structure and immunogenic properties of MPERp, a peptide vaccine that includes the following: (i) the complete sequence protected from proteolysis by the 2F5 paratope; (ii) downstream residues postulated to establish weak contacts with the CDR-H3 loop of the antibody, which are believed to be crucial for neutralization; and (iii) an aromatic rich anchor to the membrane interface. MPERp structures solved in dodecylphosphocholine micelles and 25% 1,1,1,3,3,3-hexafluoro-2-propanol (v/v) confirmed folding of the complete 2F5 epitope within continuous kinked helices. Infrared spectroscopy (IR) measurements demonstrated the retention of main helical conformations in immunogenic formulations based on alum, Freund's adjuvant, or two different types of liposomes. Binding to membrane-inserted MPERp, IR, molecular dynamics simulations, and characterization of the immune responses further suggested that packed helical bundles partially inserted into the lipid bilayer, rather than monomeric helices adsorbed to the membrane interface, could encompass effective MPER peptide vaccines. Together, our data constitute a proof-of-concept to support MPER-based peptides in combination with liposomes as stand-alone immunogens and suggest new approaches for structure-aided MPER vaccine development.

Design of monomeric water-soluble β-hairpin and β-sheet peptides

Since the first report in 1993 (JACS 115, 5887-5888) of a peptide able to form a monomeric β-hairpin structure in aqueous solution, the design of peptides forming either β-hairpins (two-stranded antiparallel β-sheets) or three-stranded antiparallel β-sheets has become a field of growing interest and activity. These studies have yielded great insights into the principles governing the stability and folding of β-hairpins and antiparallel β-sheets. This chapter provides an overview of the reported β-hairpin/β-sheet peptides focussed on the applied design criteria, reviews briefly the factors contributing to β-hairpin/β-sheet stability, and describes a protocol for the de novo design of β-sheet-forming peptides based on them. Guidelines to select appropriate turn and strand residues and to avoid self-association are provided. The methods employed to check the success of new designed peptides are also summarized. Since NMR is the best technique to that end, NOEs and chemical shifts characteristic of β-hairpins and three-stranded antiparallel β-sheets are given.