Loop substitution as a tool to identify active sites of interleukin-1 beta

The Role of Adjuvants in the Efficacy of a Peptide Vaccine for Myasthenia Gravis

Myasthenia gravis (MG) and its animal model, experimental autoimmune (EA) MG, are caused by interference with neuromuscular transmission by autoantibodies against the nicotinic acetylcholine receptor (AChR) on muscle. Previously, we have shown that two peptides, denoted RhCA 67-16 and RhCA 611-001, designed to be complementary in structure to the main immunogenic region and the dominant Lewis rat T cell epitope (α-chain residues 100-116) of the AChR, respectively, are effective vaccines that prevent EAMG in rats by inducing anti-idiotypic/clonotypic antibodies (Ab) and lowering levels of AChR Ab. These studies employed keyhole limpet hemocyanin (KLH) as a carrier and complete Freunds adjuvant (CFA). In advance of a clinical trial the present study tested the efficacy of RhCA 611-001 when combined with different adjuvants that are approved for use in humans. Adjuvants chosen for comparison were incomplete Freunds adjuvant (IFA) and aluminum hydroxide (Alum). As a second goal we evaluated diphtheria toxin (DT) as an alternative carrier protein to KLH. Alum was found to be an effective adjuvant, particularly when used with the peptide conjugated to DT. This combination of carrier and adjuvant provided protection against EAMG comparable with that observed with CFA and KLH. Using enzyme-linked immunosorbent assays for Ab against RhCA 611-001, it was found that disease protection is qualitatively, but not quantitatively, related to the anti-peptide Ab response. Our results demonstrate a vaccine formulation that should be useful in the first soon-to-be-conducted clinical trials of peptide vaccines to specifically correct aberrant T and B cell responses in an autoimmune disease.

Prevention and reversal of experimental autoimmune myasthenia gravis by a monoclonal antibody against acetylcholine receptor-specific T cells

We have recently described an algorithm to design, among others, peptides with complementarity contour to autoimmune epitopes. Immunization with one such peptide resulted in a monoclonal antibody (mAb), termed CTCR8, that specifically recognized Vbeta15 containing TCR on acetylcholine receptor (AChR) alpha-chain residue 100-116-specific T cells. CTCR8 was found to label the cell surface of AChR100-116-specific T cell lines and clones, immunoprecipitate the TCR from such cells, and block their proliferative responses to AChRalpha100-116. In the present report, we have found that there is a marked reduction in IFN-gamma and no effect on IL-10 production in a CTCR8-treated AChRalpha100-116-specific T cell line. Interestingly, when AChR100-116-primed, primary T cells were stimulated with peptide and treated with CTCR8, there was once again inhibition of IFN-gamma but also marked stimulation of IL-10 production. The change in the Th1/Th2 cytokine profile was paralleled by a reduction in AChR-specific IgG2a and IgM with no effect on IgG1. Remarkably, the most profoundly inhibited Ab population was that which causes experimental autoimmune myasthenia gravis (EAMG) by reaction with the main immunogenic region (alpha61-76) of the AChR. Based on these results, CTCR8 was tested for prophylactic and therapeutic effects in EAMG. EAMG induced by immunization with purified native Torpedo AChR was both inhibited and reversed by CTCR8. These findings suggest a means to produce therapeutic mAb for the treatment of autoimmune diseases.

A monoclonal antibody directed against the neurokinin-1 receptor contains a peptide sequence with similar hydropathy and functional properties to substance P, the natural ligand for the receptor

Monoclonal antibody (mAb) PS12, obtained using the complementary peptide methodology, mimics the neuropeptide substance P (SP) in recognizing the SP-binding domain of the neurokinin-1 receptor (NK1R) and eliciting production of polyclonal antibodies cross-reacting with SP with a high affinity (Déry et al., 1997. J. Neuroimmunol. 76, 1-9). The aim of the present study was to investigate which structural features of mAb PS12 might account for this molecular mimicry. Cloning and sequencing of variable regions of both light (VL) and heavy (VH) chains of this 'SP-like' antibody did not indicate any primary sequence homology between SP and any antibody region. Instead, they revealed a striking similarity between the hydropathic profile of SP and that of an 11-amino-acid region in the light chain encompassing the second complementarity determining region (CDR2). When applied to CHO cells expressing the human NK1R, a synthetic extended 17-amino-acid peptide (denoted CDR2L) corresponding to this VL region inhibited the high-affinity binding of radiolabeled SP and antagonized the SP-induced inositol phosphate production. Moreover, a re-examination of the sequences of several antibodies that previously served in the design of CDR-derived bioactive peptides indicated that these antibodies also carried the hydropathic image of the respective ligands that they mimic. In agreement with previous observations on artificial synthetic peptides, our data thus suggest that the molecular mimicry between natural proteins (i.e. antibody and hormone, for example) could be understood on a structural level directly related, at least in part, to hydropathic homology. These results could then guide the search for bioactive paratope-derived peptides of potential pharmacological interest. We also observed inverse hydropathy between multiple CDRs of mAb PS12 (including CDR3H and CDR3L) and the peptide epitope, confirming the importance of hydropathic complementarity in antigen-antibody interactions.

De novo design of peptides targeted to the EF hands of calmodulin

This report describes the use of the concept of inversion of hydropathy patterns to the de novo design of peptides targeted to a predetermined site on a protein. Eight- and 12-residue peptides were constructed with the EF hands or Ca(2+)-coordinating sites of calmodulin as their anticipated points of interaction. These peptides, but not unrelated peptides nor those with the same amino acid composition but a scrambled sequence, interacted with the two carboxyl-terminal Ca(2+)-binding sites of calmodulin as well as the EF hands of troponin C. The interactions resulted in a conformational change whereby the 8-mer peptide-calmodulin complex could activate phosphodiesterase in the absence of Ca(2+). In contrast, the 12-mer peptide-calmodulin complex did not activate phosphodiesterase but rather inhibited activation by Ca(2+). This inhibition could be overcome by high levels of Ca(2+). Thus, it would appear that the aforementioned concept can be used to make peptide agonists and antagonists that are targeted to predetermined sites on proteins such as calmodulin.

A peptide vaccine that prevents experimental autoimmune myasthenia gravis by specifically blocking T cell help

Myasthenia gravis (MG) and its animal model, experimental autoimmune (EA) MG, are caused by T cell-dependent autoantibodies that react with the nicotinic acetylcholine receptor (AChR) on muscle and interfere with neuromuscular transmission. Thus, selective inactivation of CD4(+) AChR-specific T helper cells should lower AChR Ab levels and ameliorate disease. In the Lewis rat model of EAMG, alpha chain residues 100-116 of the AChR represent the dominant T cell epitope, which is important in helping Ab responses to this autoantigen. In the present report, we have applied a new design technique that requires no knowledge of Ag receptor sequences on errant T cells in order to develop a synthetic peptide vaccine against T cells reactive with the aforementioned T cell epitope. Immunization with the peptide 1) induced polyclonal and monoclonal Ab, which inhibited AChR 100-116 stimulation of AChR-sensitized lymphocytes and recognized Vbeta15 containing T cell receptors on AChR 100-116-specific T cell lines and clones; 2) lowered AChR Ab levels; 3) reduced the loss of muscle AChR; and 4) lessened the incidence and severity of EAMG. These findings suggest a new strategy for the functional abrogation of epitope-specific T cells that could have potential application to human autoimmune diseases.

Synthetic alleles at position 121 define a functional domain of human interleukin-1 beta

The non-conservative substitution of the tyrosine residue at position 121 of human interleukin-1 beta (IL-1 beta) generates protein mutants showing strong reduction of the capacity to induce (a) prostaglandin E2 (PGE2) release from fibroblasts and smooth muscle cells, (b) murine T-cells proliferation and (c) activation of interleukin-6 (IL-6) gene expression. It is generally accepted that these functions are mediated by the type-I interleukin-1 receptor (IL-1RI). However, the mutant proteins maintain the binding affinity to the types-I and II IL-1 receptors, which is the same as the control IL-1 beta, suggesting that this amino acid substitution does not alter the structure of the molecule, except locally. Thus we have identified a new functional site of IL-1 beta different from the known receptor binding region, responsible for fundamental IL-1 beta functions. Moreover, we show that the same mutants maintain at least two hypothalamic functions, that is, the in vitro short-term PGE2 release from rat hypothalamus and the induction of fever in rabbits. This result suggests that there is yet another site of the molecule responsible for the hypothalamic functions, implying that multiple active sites on the IL-1 beta molecule, possibly binding to more than one receptor chain, trigger different signals.

Complementary peptides as recognition molecules

The possibility of designing sequence-directed recognition peptides (complementary peptides) able to non covalently associate target peptides or proteins is one of the most important applications deriving from the Molecular Recognition Theory [MRT]. Complementary peptides can be used widely not only as synthetic ligands for the development of affinity purification strategies to isolate target peptides or proteins from crude sources, but more importantly as peptidyl antagonists to inhibit biologically relevant interactions, or to probe functional sites in proteins and corresponding receptors.

Synthetic inducible biological response amplifiers (SIBRAs): rational peptides at the crossroads between molecular evolution and structure-based drug design

The present study proposes a novel type of synthetic chimaeric polypeptides potentially useful in the therapy of various diseases. The prototype peptide termed 'synthetic inducible biological response amplifier' (SIBRA) would comprise a ligand-binding site, a DNA-binding region, a trans-activating domain as well as strings of residues ensuring bioavailability and targeting to specific compartments such as the cell nucleus. These domains would be selected from cellular proteins, artificially tailored to a SIBRA and further modified towards a molecule with both in vivo and intracellular activity. Since proposed to resemble a host molecule with autoregulatory properties, a SIBRA would be activated upon exposure to a defined environmental stimulus and amplify host responses appropriate for this stimulus. Proteins would accumulate that share functional domains with the administered SIBRA and have a positive autoregulatory capacity. The latter may involve the interaction of the induced protein with the promoter of its gene resulting in a direct positive autoregulatory loop or require the induction of intermediary proteins that eventually upregulate the production of SIBRA-like host proteins. Since the ligand-binding site of a SIBRA is rationally designed to target a pathogenic protein, SIBRAs could be regarded as the product of an artificial acceleration and refinement of strategies intrinsic to the immune system.

Solution structure of human interleukin-1 receptor antagonist protein

Interleukin-1 receptor antagonist protein (IRAP) is a naturally occurring inhibitor of the interleukin-1 receptor. In contrast to IL-1 beta, IRAP binds to the IL-1 receptor but does not elicit a physiological response. We have determined the solution structure of IRAP using NMR spectroscopy. While the overall topology of the two 153-residue proteins is quite similar, functionally critical differences exist concerning the residues of the linear amino acid sequence that constitute structurally homologous regions in the two proteins. Structurally homologous residues important for IL-1 receptor binding are conserved between IRAP and IL-1 beta. By contrast, structurally homologous residues critical for receptor activation are not conserved between the two proteins.