Solution structure of a retro-inverso peptide analogue mimicking the foot-and-mouth disease virus major antigenic site. Structural basis for its antigenic cross-reactivity with the parent peptide

Peptide and protein mimetics by retro and retroinverso analogs

Retroinverso analog of a natural polypeptide can sometimes mimic the structure and function of the natural peptide. The additional advantage of using retroinverso analog is that it is resistant to proteolysis. The retroinverso analogs have peptide sequence in reverse direction with respect to natural peptide and also have chirality of amino acid inverted from L to D. The D amino acids cannot be recognized by common proteases of the body; therefore, these peptides will not be degraded easily and have a longer-lasting effect as vaccine and inhibitor drugs. There have been many contested propositions about the geometric relationship between a peptide and its retro, inverso, or retroinverso analog. A retroinverso analog sometimes fails to adopt the structure that can mimic the function of the natural peptide. In such cases, partial retroinverso analog and other modifications can help in achieving the desired structure and function. Here, we review the theory, major experimental attempts, prediction methods, and alternative strategies related to retroinverso peptidomimetics.

A retro-inverso cell-penetrating peptide for siRNA delivery

Background

Small interfering RNAs (siRNAs) are powerful tools to control gene expression. However, due to their poor cellular permeability and stability, their therapeutic development requires a specific delivery system. Among them, cell-penetrating peptides (CPP) have been shown to transfer efficiently siRNA inside the cells. Recently we developed amphipathic peptides able to self-assemble with siRNAs as peptide-based nanoparticles and to transfect them into cells. However, despite the great potential of these drug delivery systems, most of them display a low resistance to proteases.

Results

Here, we report the development and characterization of a new CPP named RICK corresponding to the retro-inverso form of the CADY-K peptide. We show that RICK conserves the main biophysical features of its L-parental homologue and keeps the ability to associate with siRNA in stable peptide-based nanoparticles. Moreover the RICK:siRNA self-assembly prevents siRNA degradation and induces inhibition of gene expression.

Conclusions

This new approach consists in a promising strategy for future in vivo application, especially for targeted anticancer treatment (e.g. knock-down of cell cycle proteins).Graphical abstract

D-Peptides as Recognition Molecules and Therapeutic Agents

Over recent years, D-peptides have attracted increasing attention. D-peptides increase enzymatic stability, prolong the plasma half-life, improve oral bioavailability, and enhance binding activity and specificity with receptor or target proteins, in comparison with the corresponding L-peptide. Therefore, D-peptides are considered to have potential as recognition molecules and therapeutic agents. This review focuses on the design and application of D-peptides with biological activity.

Characterization of the cell penetrating properties of a human salivary proline-rich peptide

Saliva contains hundreds of small proline-rich peptides most of which derive from the post-translational and post-secretory processing of the acidic and basic salivary proline-rich proteins. Among these peptides we found that a 20 residue proline-rich peptide (p1932), commonly present in human saliva and patented for its antiviral activity, was internalized within cells of the oral mucosa. The cell-penetrating properties of p1932 have been studied in a primary gingival fibroblast cell line and in a squamous cancer cell line, and compared to its retro-inverso form. We observed by mass-spectrometry, flow cytometry and confocal microscopy that both peptides were internalized in the two cell lines on a time scale of minutes, being the natural form more efficient than the retro-inverso one. The cytosolic localization was dependent on the cell type: both peptide forms were able to localize within nuclei of tumoral cells, but not in the nuclei of gingival fibroblasts. The uptake was shown to be dependent on the culture conditions used: peptide internalization was indeed effective in a complete medium than in a serum-free one allowing the hypothesis that the internalization could be dependent on the cell cycle. Both peptides were internalized likely by a lipid raft-mediated endocytosis mechanism as suggested by the reduced uptake in the presence of methyl-ß-cyclodextrin. These results suggest that the natural peptide may play a role within the cells of the oral mucosa after its secretion and subsequent internalization. Furthermore, lack of cytotoxicity of both peptide forms highlights their possible application as novel drug delivery agents.

Three-dimensional structure of foot-and-mouth disease virus and its biological functions

Foot-and-mouth disease (FMD), an acute, violent, infectious disease of cloven-hoofed animals, remains widespread in most parts of the world. It can lead to a major plague of livestock and an economical catastrophe. Structural studies of FMD virus (FMDV) have greatly contributed to our understanding of the virus life cycle and provided new horizons for the control and eradication of FMDV. To examine host-FMDV interactions and viral pathogenesis from a structural perspective, the structures of viral structural and non-structural proteins are reviewed in the context of their relevance for virus assembly and dissociation, formation of capsid-like particles and virus-receptor complexes, and viral penetration and uncoating. Moreover, possibilities for devising novel antiviral treatments are discussed.

Integrating the intrinsic conformational preferences of noncoded α-amino acids modified at the peptide bond into the noncoded amino acids database

Recently, we reported a database (Noncoded Amino acids Database; http://recerca.upc.edu/imem/index.htm) that was built to compile information about the intrinsic conformational preferences of nonproteinogenic residues determined by quantum mechanical calculations, as well as bibliographic information about their synthesis, physical and spectroscopic characterization, the experimentally established conformational propensities, and applications (Revilla-López et al., J Phys Chem B 2010;114:7413-7422). The database initially contained the information available for α-tetrasubstituted α-amino acids. In this work, we extend NCAD to three families of compounds, which can be used to engineer peptides and proteins incorporating modifications at the--NHCO--peptide bond. Such families are: N-substituted α-amino acids, thio-α-amino acids, and diamines and diacids used to build retropeptides. The conformational preferences of these compounds have been analyzed and described based on the information captured in the database. In addition, we provide an example of the utility of the database and of the compounds it compiles in protein and peptide engineering. Specifically, the symmetry of a sequence engineered to stabilize the 3(10)-helix with respect to the α-helix has been broken without perturbing significantly the secondary structure through targeted replacements using the information contained in the database.

Peptide structure stabilization by membrane anchoring and its general applicability to the development of potent cell-permeable inhibitors

Isolated protein motifs that are involved in interactions with their binding partners can be used to inhibit these interactions. However, peptides corresponding to protein fragments tend to have no defined secondary or tertiary structure in the absence of scaffolding by the rest of protein molecule. This results in low inhibitor potency. NMR and CD spectroscopy studies of lipopeptide inhibitors of the Hedgehog pathway revealed that membrane anchoring allows the cell membrane to function as a scaffold and facilitate the folding of short peptides. In addition, lipidation enhances cell permeability and increases the concentration of the compounds near the membrane, thus facilitating potent inhibition. The general applicability of this rational approach was further confirmed by the generation of selective antagonists of the insulin-like growth factor 1 receptor with GI(50) values in the nanomolar range. Lipopeptides corresponding to protein fragments were found to serve as potent and selective inhibitors of a number of nondruggable molecular targets.

Interaction energy analysis of peptide can predict the possibilities of mimetics by its retroinverso isomer

It has been previously reported that the retroinverso analog of S peptide cannot mimic the S peptide, whereas the retroinverso analog of foot-and-mouth disease virus antigen can mimic the foot-and-mouth disease virus antigen. The structures of S peptide, foot-and-mouth disease virus antigen, and their retroinverso analogs are known. Here, we have attempted to explain the structural basis of mimetics at the level of atomic interactions by elaborating upon the Guptasarma's hypothesis. Using interaction energy analysis of S peptide and foot-and-mouth disease virus antigen, we propose that if the energy of the CO and NH backbone atoms' non-covalent interactions with all other atoms is negligible as compared with the energy of other non-covalent interactions, then the retroinverso isomer can mimic the original peptide/protein. Previous work has established that the structure of the inverso analog of a protein will be the mirror image of the protein, and it will only recognize the respective mirror image substrate/binding partner. The retro peptide conformation that can be superimposed on all side chains in any conformation of the original peptide does not exist in the conformational space of the peptides.

Structural and functional studies on Ribonuclease S, retro S and retro-inverso S peptides

Ribonuclease S peptide and S protein offer a unique complementation system to understand the finer features of molecular recognition. In the present study the S peptide (1-16), and its retro and retro-inverso analogs have been analyzed for their structural and biological attributes. RPHPLC, CD, and NMR analyses have revealed that the physicochemical and conformational properties of the S peptide are distinct from those of its retro and retro-inverso analogs. On the functional side, while the S peptide complemented the S protein to give RNase activity, was recognized by anti-S peptide antibodies and induced T cell proliferation, neither the retro nor the retro-inverso S peptides could do so.

Heterologous expression of FMDV immunodominant epitopes and HSP70 in P. pastoris and the subsequent immune response in mice

Mycobacterium tuberculosis heat shock protein70 (HSP70) is a major antigen with both chaperone and cytokine functions. It has been used as an adjuvant to induce or potentiate humoral and cellular immunity, both in the form of a mixture with peptide antigens, and as a fusion protein. We have evaluated the effects of HSP70 on foot and mouth virus (FMDV) subunit vaccines. FMDV VP1, and a synthetic multi-epitope FMDV (EG), and VP1-HSP70 and EG-HSP70 fusion proteins were all heterologously expressed in the yeast Pichia pastoris, and used as antigen in mice. The recombinant VP1 and EG alone was able to induce both humoral and marginal cell-mediated immune responses, while the HSP70 fusions markedly enhanced both the humoral and cell-mediated immune responses. The most prominent immune responses arose from vaccination with the EG-HSP70 fusion product. Both fusion protein-induced Th1-like cytokine (IFN-gamma) and Th2-like cytokine (IL-4) were identified.

Structural analogues of smoothened intracellular loops as potent inhibitors of Hedgehog pathway and cancer cell growth

Smoothened is a critical component of the Hedgehog pathway that is essential for stem cell renewal and is dysregulated in many cancer types. We have found synthetic analogues of the second and third intracellular loops of smoothened to be potent inhibitors of the Hedgehog pathway. Palmitoylated peptides as short as 10 residues inhibited melanoma cells growth with IC50 in the low nanomolar range. The compounds are promising drug candidates and convenient tools for solving mechanisms of Hedgehog signaling.

DNA vaccination against foot-and-mouth disease via electroporation: study of molecular approaches for enhancing VP1 antigenicity

BACKGROUND

Foot-and-mouth disease virus (FMDV) affects susceptible livestock animals and causes disastrous economic impact. Immunization with plasmid expressing VP1 that contains the major antigenic epitope(s) of FMDV as cytoplasmic protein (cVP1) failed to elicit full protection against FMDV challenge.

MATERIALS AND METHODS

In this study, mice were immunized via electroporation with four cDNA expression vectors that were constructed to express VP1 of FMDV, as cytoplasmic (cVP1), secreted (sVP1), membrane-anchored (mVP1) or capsid precursor protein (P1), respectively, to evaluate whether expression of VP1 in specific subcellular compartment(s) would result in better immune responses.

RESULTS

Electroporation enhanced immune responses to vectors expressing cVP1 or P1 and expedited the immune responses to vectors expressing sVP1 or mVP1. Immunization of mice via electroporation with mVP1 cDNA was better than sVP1 or cVP1 cDNA in eliciting neutralizing antibodies and viral clearance protection. Vaccination with P1 cDNA, nonetheless, yielded the best immune responses and protection among all four cDNAs that we tested.

CONCLUSIONS

These results suggest that the antigenicity of a VP1 DNA vaccine can be significantly enhanced by altering the cellular localization of the VP1 antigen. Electroporation is a useful tool for enhancing the immune responses of vectors expressing VP1 or P1. By mimicking FMDV more closely than that of transgenic VP1 and eliciting immune responses favorably toward Th2, transgenic P1 may induce more neutralizing antibodies and better protection against FMDV challenge.

Comparative studies of the capsid precursor polypeptide P1 and the capsid protein VP1 cDNA vectors for DNA vaccination against foot-and-mouth disease virus

Background

Foot‐and‐mouth disease virus (FMDV) causes a severe livestock disease, and the virus is an interesting target for virology and vaccine studies.

Materials and methods

Here we evaluated comparatively three different viral antigen‐encoding DNA sequences, delivered via two physical means (i.e., gene gun delivery into skin and electroporation delivery into muscle), for naked DNA‐mediated vaccination in a mouse system.

Results

Both methods gave similar results, demonstrating commonality of the observed DNA vaccine effects. Immunization with a cDNA vector expressing the major viral antigen (VP1) alone routinely failed to induce the production of anti‐VP1 or neutralizing antibodies in test mice. As a second approach, the plasmid L‐VP1 that produces a transgenic membrane‐anchored VP1 protein elicited a strong antibody response, but all test mice failed in the FMDV challenge experiment. In contrast, for mice immunized with the viral capsid precursor protein (P1) cDNA expression vector, both neutralizing antibodies and 80–100% protection in test mice were detected.

Conclusions

This strategy of using the whole capsid precursor protein P1 cDNA for vaccination, intentionally without the use of virus‐specific protease or other encoding genes for safety reasons, may thus be employed as a relevant experimental system for induction or upgrading of effective neutralizing antibody response, and as a convenient surrogate test system for DNA vaccination studies of FMDV and presumably other viral diseases. Copyright © 2005 John Wiley & Sons, Ltd.

Mapping the anatomy of a Plasmodium falciparum MSP-1 epitope using pseudopeptide-induced mono- and polyclonal antibodies and CD and NMR conformation analysis

Antigen structure modulation represents an approach towards designing subunit malaria vaccines. A specific epitope's alpha carbon stereochemistry, as well as its backbone topochemistry, was assessed for obtaining novel malarial immunogens. A variety of MSP-1(38-61) Plasmodium falciparum epitope pseudopeptides derived were synthesised, based on solid-phase pseudopeptide chemistry strategies; these included all-L, all-D, partially-D substituted, all-Psi-[NH-CO]-Retro, all-Psi-[NH-CO]-Retro-inverso, and Psi-[CH2NH] reduced amide surrogates. We demonstrate that specific recombinant MSP-1(34-469) fragment binding to red blood cells (RBCs) is specifically inhibited by non-modified MSP-1(42-61), as well as by its V52-L53, M51-V52 reduced amide surrogates and partial-D substitutions in K48 and E49. In vivo tests revealed that reduced amide pseudopeptide-immunised Aotus monkeys induced neutralising antibodies specifically recognising the MSP-1 N-terminus region. These findings support the role of molecular conformation in malaria vaccine development.

DEUSS: A Perdeuterated Poly(oxyethylene)-Based Resin for Improving HRMAS NMR Studies of Solid-Supported Molecules

A novel resin called DEUSS (perdeuterated poly(oxyethylene)-based solid support) has been prepared by anionic polymerization of deuterated [D4]ethylene oxide, followed by cross-linking with deuterated epichlorohydrin. DEUSS can be suspended in a wide range of solvents including organic and aqueous solutions, in which it displays a high swelling capacity. As measured by proton HRMAS of the swollen polymer, the signal intensity of the oxyethylene protons is reduced by a factor of 110 relative to the corresponding nondeuterated poly(oxyethylene)poly(oxypropylene) (POEPOP) resin, thus facilitating detailed HRMAS NMR studies of covalently linked molecules. This 1H NMR invisible matrix was used for the solid-phase synthesis of peptides, oligoureas, and a series of amides as well as their characterization by HRMAS NMR spectroscopy. On-bead NMR spectra of high quality and with resolution comparable to that of liquid samples were obtained and readily interpreted. The complete absence of the parasite resin signals will be of great advantage, for example, for the optimization of multistep solid-phase stereoselective reactions, and for the conformational study of resin-bound molecules in a large variety of solvents.

Induction of immunity in swine by purified recombinant VP1 of foot-and-mouth disease virus

VP1, a capsid protein of foot-and-mouth disease virus (FMDV), contains neutralizing epitopes of the virus. Due to its poor water solubility, recombinant Escherichia coli derived VP1 (rVP1) has previously been used mainly in a denatured form and is not well characterized. Here, using SDS to assist protein refolding and then removing SDS with a detergent removing column, we have successfully purified rVP1 in two aqueous-soluble forms, i.e. monomer and dimer. Studies showed that dimerization occurs by an inter-molecular disulfide bond between two cysteine residues at position 187 of each monomer. Heat treatment revealed that rVP1 dimer exhibited a more thermal-stable conformation than the monomeric form. Both monomeric and dimeric rVP1 reacted with anti-FMDV antibodies. Immunization studies demonstrated that vaccination of swine with either forms of rVP1 was effective in generating immune responses and protecting them from viral challenge.

A synthetic peptide containing the consensus sequence of the G-H loop region of foot-and-mouth disease virus type-O VP1 and a promiscuous T-helper epitope induces peptide-specific antibodies but fails to protect cattle against viral challenge

A pilot study was carried out in cattle to determine the immunogenicity of a synthetic consensus peptide comprising the G-H loop region of foot-and-mouth disease virus (FMDV) type-O VP1 and a non-VP1 T-helper (Th) epitope. Cattle vaccinated intramuscularly either once (n = 5) or twice (n = 4) with 50 microg of the peptide preparation at a 21-day interval developed antibodies to the peptide as determined by ELISA with the exception of one steer that received a single dose. However, neutralizing antibody titers against FMDV type-O were modest and all animals presented with clinical FMD signs upon challenge 21 days after the last vaccination. In contrast, four of the five animals inoculated with an inactivated FMD type-O commercially prepared vaccine developed neutralizing antibodies and were fully protected against clinical disease following virus challenge 21 days post-vaccination (dpv). Nucleotide sequence comparison of the VP1 region between the challenge virus and RT-PCR products recovered from a lesion of the peptide-vaccinated animal with the highest neutralizing antibody titer 5 days post-challenge (dpc) showed no evidence for selection of a neutralization-resistant mutant. We conclude that although the synthetic peptide induced an antibody response in cattle, it failed to confer protection against FMDV challenge.

Mimicry of native peptide antigens by the corresponding retro-inverso analogs is dependent on their intrinsic structure and interaction propensities

Retro-inverso (ri) analogs of model T cell and B cell epitopes were predictively designed as mimics and then assayed for activity to understand the basis of functional ri-antigenic peptide mimicry. ri versions of two MHC class I binding peptide epitopes, one from a vesicular stomatitis virus glycoprotein (VSV(p)) and another from OVA (OVAp), exhibit structural as well as functional mimicry of their native counterparts. The two ri peptides exhibit conformational plasticity and they bind to MHC class I (H-2K(b)) similar to their native counterparts both in silico and in vivo. In fact, ri-OVAp is also presented to an OVAp-specific T cell line in a mode similar to native OVAp. In contrast, the ri version of an immunodominant B cell peptide epitope from a hepatitis B virus protein, PS1, exhibits no structural or functional correlation with its native counterpart. PS1 and its ri analog do not exhibit similar conformational propensities. PS1 is less flexible relative to its ri version. These observed structure-function relationships of the ri-peptide epitopes are consistent with the differences in recognition properties between peptide-MHC vs peptide-Ab binding where, while the recognition of the epitope by MHC is pattern based, the exquisitely specific recognition of Ag by Ab arises from the high complementarity between the Ag and the binding site of the Ab. It is evident that the correlation of conformational and interaction propensities of native L-peptides and their ri counterparts depends both on their inherent structural properties and on their mode of recognition.

What to synthesize? from Emil Fischer to peptidomics

The driving forces, incentives and strategic targets of peptide synthesis have undergone considerable evolution during the centenary following the pioneer work of Emil Fischer. In those days peptide synthesis was considered as a way of confirming the polypeptide theory of protein structure. The scientific community also expected (naively) that the synthesis would eventually lead to the creation of artificial living organisms. Only in the 1950s, when the first exact amino acid sequences were established did peptide chemistry obtain firmer ground and clearly defined targets. The total synthesis of peptide hormones and antibiotics became possible, providing valuable material for elucidating structure-functional relationships and the mechanisms of biological action. In the following years the number of peptides isolated from various biological sources grew with impressive speed and peptides became known as the most abundant, ubiquitous group of low molecular bioregulators. The design and synthesis of novel peptide based pharmaceuticals became an important area of peptide chemistry. At present we are facing the challenge of analysing the structures and bioactivities of total sets of peptides, i.e. peptidoms, present in concrete tissues or groups of cells. The results obtained along these lines at the IBCH RAS Institute of Bioorganic Chemistry are briefly considered in the review.

Sequence-simplification and chimeric assembly: new models of peptide antigen modification

Sequence-simplified variants of a 15-mer peptide antigen, identified by amino acid side chains in alternating positions were synthesized introducing glycine residues alternatively in the parent peptide sequence and used to induce antibodies in rabbit. They reacted to a significant extent with anti-parent peptide antibodies, and in addition, affinity purified antibodies against these halved forms recognized with similar affinity and specificity, the starting peptide in affinity chromatography, optical biosensor and enzyme linked immunosorbent assay (ELISA) experiments, while no cross-reactivity was detected between reduced antigens. These findings suggest that a peptide antigen can display two molecular surfaces of recognition, identified by side chains of residues in alternating positions. Each surface can even take part in antigen/antibody interaction independently, thus indicating the possibility to select and assembly sequence-simplified forms belonging to different epitopes, also deriving from different molecules, to generate new structures incorporating a two-fold antigen/antibody specificity. Two "chimeric" forms were then synthesized starting from the P15 and P13 complementary peptides, both able to bind interleukin 2. These structures, showing simultaneously trans-surfaces of recognition belonging to both parent forms, have been found to retain antigenic properties against antibodies of simplified P15 derivatives showing the same molecular surface of recognition. In addition, anti-chimeric antibodies recognized both P15 and P13 starting peptides, while no cross-antibody recognition was observed between chimeric antigens.

Structural and immunological characterisation of heteroclitic peptide analogues corresponding to the 600-612 region of the HIV envelope gp41 glycoprotein

The conformational and immunological properties of different analogues corresponding to the 600-612 disulfide loop of the human immunodeficiency virus (HIV) gp41 glycoprotein envelope were studied. Fourteen analogues were designed and synthesised; namely, a series of seven analogues in which the disulfide bond was replaced by a lactam bridge and a series of seven analogues in which one residue of each analogue at a time, was replaced by its corresponding homologised alpha-amino acid (beta(3)-amino acid). In the case of the lactam analogues, the influence of the two possible CO-NH and NH-CO orientations of the lactam bridge as well as the size of the lactam ring was explored. The analogues were tested in ELISA with monoclonal antibodies raised against the 600-612 cyclic parent peptide as well as with sera from HIV-1 infected patients. A structural analysis of the parent and analogue peptides was carried out in dimethyl sulfoxide (DMSO-d(6)) using two-dimensional NMR techniques and molecular dynamics simulations. Comparison of the own conformation of the cyclic analogues with their either strong or weak reactivity with the antibodies reveals structural features that may be correlated with the antibody reactivity. Thus, a close structural similarity, particularly a characteristic orientation of the side-chains of residues Lys606, Leu607 and Ile608 in the loop, was found in certain beta(3)-analogues that were better recognised than the parent peptide by anti-peptide mouse monoclonal antibodies and patients' antibodies.

A retro-inverso peptide analogue of influenza virus hemagglutinin B-cell epitope 91-108 induces a strong mucosal and systemic immune response and confers protection in mice after intranasal immunization

In this study, a novel approach for the development of a peptide-based vaccine has been tested. We investigated the possibility of replacing an all-L amino acid peptide sequence corresponding to the protective B-cell epitope hemagglutinin (HA) 91-108 from influenza HA with a retro-inverso analogue encompassing this sequence. Retro-inverso peptides are composed of D-amino acids assembled in a reverse order from that of the parent L-sequence, thus maintaining the overall topology of the native sequence. This explains the observed antigenic cross-reactivity with anti-influenza virus antibodies. Mice immunized intranasally with the ovalbumin-conjugated retro-inverso analogue and cholera toxin as an adjuvant, produced strong systemic (serum IgG) and mucosal (lung IgA) antibody responses, and were protected against intranasal challenge with a lethal dose of influenza virus. The weight loss pattern in the protected group indicated that the vaccinated animals developed a disease of low severity resulting in a quick recovery. Furthermore, splenocytes of the immunized mice cultured in the presence of inactivated influenza virus, secreted high levels of IFN-gamma. The half-life of the retro-inverso analogue in the presence of lung homogenate proteases was at least 700 times greater than that of the parent L-peptide. These results demonstrate that peptidomimetic analogues with high resistance to proteolytic degradation are very effective immunogens when administered via the intranasal route, inducing protective immunity against a viral infection. This approach might be advantageous for vaccine development.

Proton dipolar recoupling in resin-bound peptides under high-resolution magic angle spinning

Rotational resonance and radiofrequency-driven dipolar recoupling (RFDR) experiments have been used to recover the weak proton dipolar interaction present in peptides bound to swollen resins spun at the magic angle. The intensity of the correlation peaks obtained using these sequences is shown to be significantly stronger than the one obtained using the classical NOESY experiment. In addition, it is found that during the relatively long mixing times required to transfer magnetization in such soft materials, the RFDR sequence also achieves magnetization transfer via the scalar J-coupling.

Retro-inverso peptide analogues of Trypanosoma cruzi B13 protein epitopes fail to be recognized by human sera and peripheral blood mononuclear cells

Retro inverso (RI) analogues of antigenic synthetic peptides, which are made of D-amino acids with a reversed sequence, may mimic the side chain conformation of natural all-L peptides. RI analogues were cross-reactively recognized by antibodies and CD4+ T cells reactive against natural all-L synthetic peptides or native proteins in animal models. Since peptides containing D-amino acids are highly resistant to proteolytic digestion, cross-reactive RI analogues may be ideal for in vivo administration to humans as synthetic peptide vaccines or immunomodulators. B13 is an immunodominant tandemly repetitive protein from Trypanosoma cruzi, a protozoan parasite that is the causative antigen of Chagas' disease. In order to test whether RI peptides can be recognized by human antibody and T cells, we synthesized two all-L peptides containing the immunodominant B (S12) and T (S15.7) cell epitopes of B13 protein from T. cruzi and their retro (R, made of all-L amino acids with reversed sequence), inverso (I, made of all-D amino acids) and RI analogues. Recognition of peptides S12, S12-R, S12-I and S12-RI by anti-B13 antibodies in sera from T. cruzi-infected patients was tested in competitive ELISA assay with recombinant B13 protein as the solid phase antigen. Peptides S15.7 and its topological analogues were tested at the 10-50 microM range in proliferation assays on peripheral blood mononuclear cells (PBMC) from S15.7-responder individuals. The median percentage inhibition of B13 ELISA for peptide S12 was 94%, while those of the RI analogue or the other topological analogues were below 12%. While peptide S15.7 was recognized by PBMC from all subjects tested, none recognized the RI analogue of the S15.7 T cell epitope. Our results indicate that cross-reactivity with natural epitopes is not an universal property of RI analogues. This may limit the general applicability of the use of cross-reactive RI analogues as human vaccines and immunotherapeutic agents.

The bare skin and the nose as non-invasive routes for administering peptide vaccines

Among the different technologies currently tested for the development of novel vaccines, synthetic peptides represent a promising option, since they are chemically pure and induce immune responses of predetermined specificity. Furthermore, they can be replaced with pseudopeptides or peptide mimetics that contain changes in the amide bond, resulting in more stable and immunogenic molecules. Administration of peptide vaccines via non-invasive routes, such as the nose or the bare skin, allows the efficient uptake of antigen by antigen-presenting cells, which are abundant in the associated lymphoid tissues, ensuring the induction of effective systemic and mucosal immune responses. Using non-invasive routes could be advantageous for vaccination programs in third-world countries, since vaccine administration is simple, painless and economical. In this review, we discuss and present some preliminary data on the advantages of synthetic peptides and peptidomimetics as candidate vaccines, and their potential for administration via the skin and the nose.

Survey of the 1999 surface plasmon resonance biosensor literature

The application of surface plasmon resonance biosensors in life sciences and pharmaceutical research continues to increase. This review provides a comprehensive list of the commercial 1999 SPR biosensor literature and highlights emerging applications that are of general interest to users of the technology. Given the variability in the quality of published biosensor data, we present some general guidelines to help increase confidence in the results reported from biosensor analyses.

Structure-function analysis of the 7B2 CT peptide

Prohormone convertases play important roles in the proteolytic conversion of many protein precursors. The neuroendocrine protein 7B2 and its 31-residue carboxyl-terminal (CT) peptide potently and specifically inhibit prohormone convertase 2 (PC2). We have analyzed the residues contributing to inhibition using N-terminal truncation and alanine scanning. Removal of more than 3 residues from the amino-terminal end of CT1-18 resulted in a more than 190-fold drop in inhibitory activity, showing that most of the residues between 3 and 18 are required for inhibition. In agreement, an Ala scan indicated that only 4 residues could be replaced with Ala without losing mid-nanomolar inhibitory potency; in particular, Gln7, Gln9, and Asp12 could be Ala-substituted to yield peptides with a similar inhibitory potency to the starting peptide. The all-d-retro-inverso, all-l-inverso, and all-d analogues of CT peptide were completely inactive, indicating that amino acid side chains and the CT peptide main chain interact with PC2. CT peptide inhibition could not be competitively blocked by preincubation with truncated CT peptide forms, supporting an absolute requirement for the Lys-Lys pair in initial binding of the CT peptide to the active site.