Direct synthesis and characterisation of multi-dendritic peptides for use as immunogens

How well can a T-cell epitope replace its parent carrier protein? A dose-response study

PURPOSE

This work examines the effectiveness of synthetic peptide immunogens derived from immunodominant T-cell epitopes as replacements for their intact parent protein in vaccines.

METHODS

Fluorescein was conjugated to hen egg lysozyme (FL-HEL, positive control) and three synthetic peptide immunogens: (a) murine B10.A (H-2a) immunodominant T-cell epitope of HEL [FL-(T-cell epitope)]; (b) multiple antigenic peptide (MAP) multimer of this epitope ([FL-(T epitope)]n-MAP, n = 2-4); and (c) negative control MAP with T-cell epitope residues replaced with glycine [(FL-Gly18)4-MAP]. The dose response of each immunogen was examined over a 300-fold range in B10.A mice. The immune response was monitored using antifluorescein ELISA assays.

RESULTS

FL-(T epitope)'s immune response correlated positively with dose, with maximum response comparable to that of [FL-(T epitope)]n-MAP, or FL-HEL. This trend was consistent across 1 degrees, 2 degrees, and 3 degrees responses, although interanimal variability was higher in the latter two because of an all-or-none response in mice immunized with this peptide. [FL-(T epitope)]n-MAP's immune response was consistently high and nearly dose independent, a trend observed across 1 degrees, 2 degrees, and 3 degrees responses. FL-HEL's immune response correlated negatively to dose in the 1 degrees response but was nearly dose independent in the 2 degrees and 3 degrees responses. The magnitude of these latter responses was comparable to that observed for [FL-(T epitope)]n-MAP. (FL-Gly18)4-MAP did not elicit an immune response except at the highest dose. This trend was consistent across 1 degrees, 2 degrees, and 3 degrees responses.

CONCLUSIONS

The monomeric epitope was 300-fold less potent than its parent carrier protein, but increasing immunogen valency using MAP technology compensated totally for reduced potency. (FL-Gly18)4-MAP's lack of response at all but the highest dose strongly suggests that a specific immunodominant T-cell epitope sequence for HEL is necessary for successful peptide mimicry of HEL. This work also demonstrates the importance of quality assessment of commercial MAP core resins.

Thermodynamic assessment of the stability of thrombin receptor antagonistic peptides in hydrophobic environments

In this paper, a general procedure is described to determine thermodynamic parameters associated with the interaction of thrombin receptor antagonistic peptides (TRAPs) with immobilized nonpolar ligands. The results show that these interactions were associated with nonlinear van't Hoff dependencies over a wide temperature range. Moreover, changes in relevant thermodynamic parameters, namely the changes in Gibbs free energy of interaction, DeltaG(0)assoc, enthalpy of interaction, DeltaH(0)assoc, entropy of interaction, DeltaS(0)assoc, and heat capacity, DeltaC(0)p, have been related to the structural properties of these TRAP analogs. The implications of these investigations for the design of thrombin receptor agonists/antagonists with structures stabilized by intramolecular hydrophobic interactions are discussed.

Total chemical synthesis of human activin beta(A)[12-116] and related large-loop polypeptides

We report here the synthesis, purification, and characterization of several large polypeptides related to the human activin beta(A) subunit and their cyclic counterparts. In particular, we describe for the first time the total chemical synthesis of a 105-mer polypeptide, des[1-11] activin beta(A), and related large-loop polypeptide, by an optimized solid phase synthetic protocol based on 9-flouroenylmethyoxycarbonyl (Fmoc) chemistry. These studies show that automated chemical synthesis utilizing Fmoc-based solid phase synthetic strategies provides a practical alternative to recombinant DNA technology for the production of activin-related subunits, with the opportunity to rapidly provide different analogues and structural variants for subsequent structure-function and associated biophysical investigations.

Double dimer peptide constructs are immunogenic and protective against Plasmodium falciparum in the experimental Aotus monkey model

Multiple antigen peptide constructs (MAPs) have been used to obtain defined multimeric peptide molecules useful in the development of possible synthetic malaria vaccines. In this context, a method was developed, named double dimer constructs (DDCs), involving the direct synthesis of a dimeric peptide with a C-terminal cysteine. A tetrameric molecule was then obtained by oxidation of sulfhydryl groups. Dimer synthesis was optimized using a Fmoc/tBu strategy, dimers were purified by HPLC, oxidized with DMSO and characterized by HPLC and MALDI-TOF-MS. The tetramers or DDCs obtained by this method were used as immunogens in the search for a possible malaria vaccine. It was found that they were immunogenic in the experimental Aotus monkey model, and were able to induce protective immunity when challenged experimentally with a highly infective Plasmodium falciparum malaria strain.

Peptide analysis by rapid, orthogonal technologies with high separation selectivities and sensitivities

This article examines the current status of peptide analysis by orthogonal micro-/nano-separation strategies, with emphasis on the complementary use of high performance capillary liquid chromatography (micro-HPLC), capillary zonal electrophoresis (HPCZE), open tubular capillary electrochromatography (ot -CEC) and packed capillary electrochromatography (p -CEC). The ability to interface these techniques with mass spectroscopic (MS) procedures has enabled substantial progress to be made in the analysis of very small quantities of peptides, as well as proteins and other bio-macromolecules. As a consequence, the staged application of these high resolution techniques as part of the standardisation of biological products via robust, sensitive protocols is rapidly becoming a reality. Recent conceptual and theoretical advances have also allowed improved levels of prediction and optimisation of these procedures. Since significant differences in selectivity can be achieved with micro-HPLC, HPCZE and HPCEC respectively, collectively these sophisticated techniques provide unprecedented opportunities for the rapid, orthogonal and sensitive separation of complex mixtures of peptides and proteins. Several advantages of using these technologies in tandem are highlighted.

Synthesis and application of peptide immunogens related to the sperm tail protein tpx-1, a member of the CRISP superfamily of proteins

The synthesis of peptides containing 0, 1 and 2 cysteine residues related to the human sperm tail protein, tpx-1, is described. These synthetic peptides, following conjugation to keyhole limpet hemocyanin modified with maleimidobenzoic acid N-hydroxysuccinimide ester, were used as immunogens to generate polyclonal antibodies in female New Zealand white rabbits. The binding characteristics of the derived antipeptide sera were evaluated using indirect and competitive ELISA procedures. Western immunoblot experiments also confirmed that these synthetic peptide immunogens are able to generate high-titer polyclonal antibodies capable of cross-reacting with the mature tpx-1 protein present in crude rat sperm tail/testis preparations as well as in outer dense fiber preparations. Consequently, these synthetic peptides represent promising candidates for investigations into the role of tpx-1 in the immunoregulation of sperm function in the rat and other mammalian models, with the derived antisera also providing an avenue to explore possible sites of expression of tpx-1 proteins in other tissues.

Direct characterisation by electrospray ionisation mass spectroscopy of mercuro-polypeptide complexes after deprotection of acetamidomethyl groups from protected cysteine residues of synthetic polypeptides

In this paper, we describe a rapid procedure to characterise the products generated in the presence of mercuric salts following removal of the acetamidomethyl (Acm)-protecting group from cysteine residues of synthetic polypeptides prepared by solid-phase peptide synthesis (SPPS) methods. In particular, electrospray ionisation mass spectrometry (ESI-MS) procedures have been employed to characterise the mercuro-polypeptide products related to the ribosomal L36 protein isolated from the bacterium Thermus thermophilus. The results demonstrate that very stable mercuro-polypeptide complexes can form under standard conditions of deprotection involving Hg(2+) salts in the presence of a reductant such as beta-mercaptoethanol. Metal ion exchange effects involving other divalent metal ions, such as Co(2+) or Zn(2+), can also be monitored by similar procedures, thus permitting the relative affinity and selectivity for metal ion-polypeptide interactions to be qualitatively assessed. Since the Thermus thermophilus ribosomal L36 protein contains a putative zinc finger binding CCCH motif, these procedures enable the formation of metal-ion complexes of synthetic polypeptides related to this structural motif to be directly examined.

Ligand-presenting assembly: a method for C- and N-terminal antigen presentation

Achiral dicarboxylic acids were coupled with 2 eq. of the free alpha-amino groups of two fully side-chain protected peptide chains while these were still attached to a synthesis resin. Cleavage from the resin with simultaneous side-chain deprotection afforded two assembled peptide chains with free C-terminals. Suitable functionalization of the achiral dicarboxylic acid alternatively permitted continued peptide synthesis in a C to N orientation leading to a final peptide assembly which, after cleavage from the resin, may have multiple N to C and C to N presentation of one or more epitopes.

Studies on the relationship between structure and electrophoretic mobility of alpha-helical and beta-sheet peptides using capillary zone electrophoresis

The electrophoretic behaviour of a series of 33 different synthetic peptides has been investigated using free solution high-performance capillary zonal electrophoretic (HPCZE) methods. The dependency of the electrophoretic mobility, mu(em), on the peptide charge, q, and on the charge-to-size ratio parameter, zeta, determined according to several electromobility models, have been examined. Significant divergences from linearity in the mu(em) vs. q or the mu(em) vs. zeta plots were noted for several peptides, possibly due to the proclivity of specific arrangements of their amino acid sequences to assume preferred alpha-helical or beta-sheet conformational features rather than random coil structures under the HPCZE conditions. These results provide further demonstration of the facility of HPCZE procedures to probe the effects of compositional, sequential and conformational differences of closely-related peptides and their consequences on their physicochemical behaviour in solution.

Peptide and glycopeptide dendrimers. Part II

Recent progress in peptide and glycopeptide chemistry make the preparation of peptide and glycopeptide dendrimers of acceptable purity, with designed structural and immunochemical properties reliable. New methodologies using unprotected peptide building blocks have been developed to further increase the possibilities of their design and improve their preparation and separation. The sophisticated design of peptide and glycopeptide dendrimers has led to their use as antigens and immunogens, for serodiagnosis and other biochemical uses including drug delivery. Dendrimers bearing peptide with predetermined secondary structures are useful tools in protein de novo design. This article covers synthesis and applications of multiple antigen peptides (MAPs), multiple antigen glycopeptides (MAGs), multiple antigen peptides based on sequential oligopeptide carriers (MAP-SOCs), glycodendrimers and template-assembled synthetic proteins (TASPs). In part II the preparation of MAPs, and the utility of glycodendrimers and TASPs are discussed.

Observations on the origin of the non-linear van't Hoff behaviour of polypeptides in hydrophobic environments

In this paper we describe a general procedure to determine the thermodynamic parameters associated with the interaction of polypeptides or proteins with immobilised lipophilic compounds such as non-polar n-octyl groups. To this end, the binding behaviour of an all L-alpha-polypeptide, 1, and its retro-inverso-isomer, 2, has been investigated with an n-octylsilica and water-organic solvent mixture containing different percentages of acetonitrile or methanol over the temperature range of 278-338 K. The results confirm that non-linear van'ts Hoff plots occur with this pair of polypeptide isomers, depending on the solvent composition. These findings are consistent with the changes in the thermodynamic parameters, enthalpy of association, delta Hoassoc,i, entropy of association, delta Soassoc,i, and heat capacity, delta Cop,i, all having significant temperature dependencies. Theoretical relationship linking the changes in the delta Hoassoc,i, delta Soassoc,i and delta Cop,i values of these polypeptide-non-polar ligate systems, as a function of temperature, T, have been validated. Significant differences were observed in the magnitudes of these thermodynamic quantities when acetonitrile or methanol was employed as the organic solvent. The origin of these solvent-dependent effects can be attributed to the hydrogen-bonding propensity of the respective solvent. Involvement of enthalpy-entropy compensation effects associated with the interaction of these polypeptides with the hydrophobic ligates has also been documented. Analysis of empirical extra-thermodynamic relationships associated with molecular structural properties of these polypeptides, such as the slope term, S, derived from the plots of the logarithmic capacity factor, log k'i, of these polypeptides vs. the volume fraction of the organic solvent, [symbol: see text] as a function of temperature, T, has also revealed similar correlations in terms of the interactive behaviour of polypeptides 1 and 2 under these experimental conditions. These findings provide an extended thermodynamic and extra-thermodynamic framework to examine the solvational, conformational and other equilibrium processes that polypeptides (or proteins) can undergo in the presence of n-alkylsilicas or other classes of immobilised hydrophobic surfaces. The experimental approach utilised in this study with these topologically similar polypeptides thus represents a generic procedure to explore the behaviour of polypeptides or proteins in non-polar environments in terms of their molecular properties and the associated linear free energy relationships that determine their interactive behaviour.