Treatment of experimental allergic encephalomyelitis (EAE) by a rationally designed cyclic analogue of myelin basic protein (MBP) epitope 72-85

An Overview of Peptide-Based Molecules as Potential Drug Candidates for Multiple Sclerosis

Multiple sclerosis (MS) belongs to demyelinating diseases, which are progressive and highly debilitating pathologies that imply a high burden both on individual patients and on society. Currently, several treatment strategies differ in the route of administration, adverse events, and possible risks. Side effects associated with multiple sclerosis medications range from mild symptoms, such as flu-like or irritation at the injection site, to serious ones, such as progressive multifocal leukoencephalopathy and other life-threatening events. Moreover, the agents so far available have proved incapable of fully preventing disease progression, mostly during the phases that consist of continuous, accumulating disability. Thus, new treatment strategies, able to halt or even reverse disease progression and specific for targeting solely the pathways that contribute to the disease pathogenesis, are highly desirable. Here, we provide an overview of the recent literature about peptide-based systems tested on experimental autoimmune encephalitis (EAE) models. Since peptides are considered a unique therapeutic niche and important elements in the pharmaceutical landscape, they could open up new therapeutic opportunities for the treatment of MS.

Characterization of Asparagine Deamidation in Immunodominant Myelin Oligodendrocyte Glycoprotein Peptide Potential Immunotherapy for the Treatment of Multiple Sclerosis

Mannan (polysaccharide) conjugated with a myelin oligodendrocyte glycoprotein (MOG) peptide, namely (KG)5MOG35-55, represents a potent and promising new approach for the immunotherapy of Multiple Sclerosis (MS). The MOG35-55 epitope conjugated with the oxidized form of mannan (poly-mannose) via a (KG)5 linker was found to inhibit the symptoms of MOG35-55-induced experimental autoimmune encephalomyelitis (EAE) in mice using prophylactic and therapeutic vaccinated protocols. Deamidation is a common modification in peptide and protein sequences, especially for Gln and Asn residues. In this study, the structural solution motif of deaminated peptides and their functional effects in an animal model for MS were explored. Several peptides based on the MOG35-55 epitope have been synthesized in which the Asn53 was replaced with Ala, Asp, or isoAsp. Our results demonstrate that the synthesized MOG peptides were formed to the deaminated products in basic conditions, and the Asn53 was mainly modified to Asp. Moreover, both peptides (wild type and deaminated derivative) conjugated with mannan (from Saccharomyces cerevisiae) independently inhibited the development of neurological symptoms and inflammatory demyelinating spinal cord lesions in MOG35-55-induced EAE. To conclude, mannan conjugated with a deamidated product did not affect the efficacy of the parent peptide.

A Journey to the Conformational Analysis of T-Cell Epitope Peptides Involved in Multiple Sclerosis

Multiple sclerosis (MS) is a serious central nervous system (CNS) disease responsible for disability problems and deterioration of the quality of life. Several approaches have been applied to medications entering the market to treat this disease. However, no effective therapy currently exists, and the available drugs simply ameliorate the destructive disability effects of the disease. In this review article, we report on the efforts that have been conducted towards establishing the conformational properties of wild-type myelin basic protein (MBP), myelin proteolipid protein (PLP), myelin oligodendrocyte glycoprotein (MOG) epitopes or altered peptide ligands (ALPs). These efforts have led to the aim of discovering some non-peptide mimetics possessing considerable activity against the disease. These efforts have contributed also to unveiling the molecular basis of the molecular interactions implicated in the trimolecular complex, T-cell receptor (TCR)–peptide–major histocompatibility complex (MHC) or human leucocyte antigen (HLA).

The Long Road of Immunotherapeutics against Multiple Sclerosis

This commentary highlights novel immunomodulation and vaccine-based research against multiple sclerosis (MS) and reveals the amazing story that triggered this cutting-edge MS research in Greece and worldwide. It further reveals the interest and solid support of some of the world's leading scientists, including sixteen Nobel Laureates who requested from European leadership to take action in supporting Greece and its universities in the biggest ever financial crisis the country has encountered in the last decades. This support endorsed vaccine-based research on MS, initiated in Greece and Australia, leading to a worldwide network aiming to treat or manage disease outcomes. Initiatives by bright and determined researchers can result in frontiers science. We shed light on a unique story behind great research on MS which is a step forward in our efforts to develop effective treatments for MS.

A Cyclic Altered Peptide Analogue Based on Myelin Basic Protein 87-99 Provides Lasting Prophylactic and Therapeutic Protection Against Acute Experimental Autoimmune Encephalomyelitis

In this report, amide-linked cyclic peptide analogues of the 87-99 myelin basic protein (MBP) epitope, a candidate autoantigen in multiple sclerosis (MS), are tested for therapeutic efficacy in experimental autoimmune encephalomyelitis (EAE). Cyclic altered peptide analogues of MBP_87-99 with substitutions at positions 91 and/or 96 were tested for protective effects when administered using prophylactic or early therapeutic protocols in MBP_72-85-induced EAE in Lewis rats. The Lys⁹¹ and Pro⁹⁶ of MBP_87-99 are crucial T-cell receptor (TCR) anchors and participate in the formation of trimolecular complex between the TCR-antigen (peptide)-MHC (major histocompability complex) for the stimulation of encephalitogenic T cells that are necessary for EAE induction and are implicated in MS. The cyclic peptides were synthesized using Solid Phase Peptide Synthesis (SPPS) applied on the 9-fluorenylmethyloxycarboxyl/tert-butyl Fmoc/tBu methodology and combined with the 2-chlorotrityl chloride resin (CLTR-Cl). Cyclo(91-99)[Ala⁹⁶]MBP_87-99, cyclo(87-99)[Ala^91,96]MBP_87-99 and cyclo(87-99)[Arg⁹¹, Ala⁹⁶]MBP_87-99, but not wild-type linear MBP_87-99, strongly inhibited MBP_72-85-induced EAE in Lewis rats when administered using prophylactic and early therapeutic vaccination protocols. In particular, cyclo(87-99)[Arg⁹¹, Ala⁹⁶]MBP_87-99 was highly effective in preventing the onset and development of clinical symptoms and spinal cord pathology and providing lasting protection against EAE induction.

Biologically relevant conformational features of linear and cyclic proteolipid protein (PLP) peptide analogues obtained by high-resolution nuclear magnetic resonance and molecular dynamics

Proteolipid protein (PLP) is one of the main proteins of myelin sheath that are destroyed during the progress of multiple sclerosis (MS). The immunodominant PLP_139-151 epitope is known to induce experimental autoimmune encephalomyelitis (EAE, animal model of MS), wherein residues 144 and 147 are recognized by T cell receptor (TCR) during the formation of trimolecular complex with peptide-antigen and major histocompability complex. The conformational behavior of linear and cyclic peptide analogues of PLP, namely PLP_139-151 and cyclic (139-151) (L¹⁴⁴, R¹⁴⁷) PLP_139-151, have been studied in solution by means of nuclear magnetic resonance (NMR) methods in combination with unrestrained molecular dynamics simulations. The results indicate that the side chains of mutated amino acids in the cyclic analogue have different spatial orientation compared with the corresponding side chains of the linear analogue, which can lead to reduced affinity to TCR. NMR experiments combined with theoretical calculations pave the way for the design and synthesis of potent restricted peptides of immunodominant PLP_139-151 epitope as well as non peptide mimetics that rises as an ultimate goal.

Immune responses of linear and cyclic PLP139-151 mutant peptides in SJL/J mice: peptides in their free state versus mannan conjugation

BACKGROUND

The predominant proteins of the CNS are myelin basic protein, proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein. PLP139-151 is one of the major encephalitogenic epitopes of PLP. The epitope PLP139-151 binds to MHC class II (I-A(s)) of SJL/J mice and induces Th1 responses.

AIM

The aim was to synthesize and test the immunological activity and cyclic analogs of PLP139-151 peptide and determine the immunological differences between adjuvant and conjugation to mannan. Materials & methods: We designed and synthesized cyclic peptides based on the linear PLP139-151 epitope by mutating critical T-cell receptor contact sites of residues W(144) and H(147), resulting in the mutant peptides PLP139-151, [L(144), R(147)]PLP139-151 or cyclo(139-151)PLP139-151 and cyclo(139-151) [L(144), R(147)]PLP139-151. In this study, mice were immunized with mutant peptides either emulsified in complete Freund's adjuvant or conjugated to reduced mannan and responses were assessed.

RESULTS

Linear double-mutant peptide [L(144), R(147)]PLP139-151 induced high levels of IL-4 responses and low levels of IgG total, and cyclization of this analog elicited low levels of IFN-γ. Moreover, linear [L(144), R(147)]PLP139-151 conjugated to reduced mannan did not induce IFN-γ, whilst both linear agonist PLP139-151 and cyclic agonist cyclo(139-151)PLP139-151 induced IFN-γ-secreting T cells. Molecular dynamics simulations of linear and cyclic(139-151)PLP139-151 analogs indicated the difference in topology of the most important for biological activity amino acids.

CONCLUSION

Cyclic double-mutant analog cyclo(139-151) [L(144), R(147)]PLP139-151 has potential for further studies for the immunotherapy of multiple sclerosis.

Mannosylated Linear and Cyclic Single Amino Acid Mutant Peptides Using a Small 10 Amino Acid Linker Constitute Promising Candidates Against Multiple Sclerosis

Multiple sclerosis (MS) is a serious autoimmune demyelinating disease leading to loss of neurological function. The design and synthesis of various altered peptide ligands of immunodominant epitopes of myelin proteins to alter the autoimmune response, is a promising therapeutic approach for MS. In this study, linear and cyclic peptide analogs based on the myelin basic protein 83–99 (MBP_83–99) immunodominant epitope conjugated to reduced mannan via the (KG)₅ and keyhole limpet hemocyanin (KLH) bridge, respectively, were evaluated for their biological/immunological profiles in SJL/J mice. Of all the peptide analogs tested, linear MBP_83–99(F⁹¹) and linear MBP_83–99(Y⁹¹) conjugated to reduced mannan via a (KG)₅ linker and cyclic MBP_83–99(F⁹¹) conjugated to reduce mannan via KLH linker, yielded the best immunological profile and constitute novel candidates for further immunotherapeutic studies against MS in animal models and in human clinical trials.

Rational design and synthesis of altered peptide ligands based on human myelin oligodendrocyte glycoprotein 35-55 epitope: inhibition of chronic experimental autoimmune encephalomyelitis in mice

Experimental autoimmune encephalomyelitis (EAE) is a demyelinating disease of the central nervous system and is an animal model of multiple sclerosis (MS). Although the etiology of MS remains unclear, there is evidence T-cell recognition of immunodominant epitopes of myelin proteins, such as the 35–55 epitope of myelin oligodendrocyte glycoprotein (MOG), plays a pathogenic role in the induction of chronic EAE. Cyclization of peptides is of great interest since the limited stability of linear peptides restricts their potential use as therapeutic agents. Herein, we have designed and synthesized a number of linear and cyclic peptides by mutating crucial T cell receptor (TCR) contact residues of the human MOG_35–55 epitope. In particular, we have designed and synthesized cyclic altered peptide ligands (APLs) by mutating Arg⁴¹ with Ala or Arg⁴¹ and Arg⁴⁶ with Ala. The peptides were synthesized in solid phase on 2-chlorotrityl chloride resin (CLTR-Cl) using the Fmoc/t-Bu methodology. The purity of final products was verified by RP-HPLC and their identification was achieved by ESI-MS. It was found that the substitutions of Arg at positions 41 and 46 with Ala results in peptide analogues that reduce the severity of MOG-induced EAE clinical symptoms in C57BL/6 mice when co-administered with mouse MOG_35–55 peptide at the time of immunization.

A novel synthetic luteinizing hormone-releasing hormone (LHRH) analogue coupled with modified β-cyclodextrin: insight into its intramolecular interactions

BACKGROUND

Cyclodextrins (CDs) in combination with therapeutic proteins and other bioactive compounds have been proposed as candidates that show enhanced chemical and enzymatic stability, better absorption, slower plasma clearance and improved dose-response curves or immunogenicity. As a result, an important number of therapeutic complexes between cyclodextrins and bioactive compounds capable to control several diseases have been developed.

RESULTS

In this article, the synthesis and the structural study of a conjugate between a luteinizing hormone-releasing hormone (LHRH) analogue, related to the treatment of hormone dependent cancer and fertility, and modified β-cyclodextrin residue are presented. The results show that both the phenyl group of tyrosine (Tyr) as well as the indole group of tryptophan (Trp) can be encapsulated inside the cyclodextrin cavity. Solution NMR experiments provide evidence that these interactions take place intramolecularly and not intermolecularly.

CONCLUSIONS

The study of a LHRH analogue conjugated with modified β-cyclodextrin via high field NMR and MD experiments revealed the existence of intramolecular interactions that could lead to an improved drug delivery.

GENERAL SIGNIFICANCE

NMR in combination with MD simulation is of great value for a successful rational design of peptide-cyclodextrin conjugates showing stability against enzymatic proteolysis and a better pharmacological profile.

Rationally designed cyclic analogues of luteinizing hormone-releasing hormone: enhanced enzymatic stability and biological properties

This article describes the rational design, synthesis and pharmacological properties of amide-linked cyclic analogues of Luteinizing Hormone-Releasing Hormone (LHRH) with substitutions at positions 1 (Pro), 6 (D-Leu/D-Trp), 9 (Aze) and 10 (BABA/Acp). These LHRH analogues fulfil the conformational requirements that are known in the literature (bend in the 5-8 segment) to be essential for receptor recognition and activation. Although, they are characterised by an overall low binding affinity to the LHRH-I receptor, the cyclic analogues that were studied and especially the cyclo(1-10)[Pro(1), D-Leu(6), BABA(10)] LHRH, exhibit a profoundly enhanced in vitro and in vivo stability and improved pharmacokinetics in comparison with their linear counterpart and leuprolide. Upon receptor binding, cyclo(1-10)[Pro(1), D-Leu(6), BABA(10)] LHRH causes testosterone release in C57/B16 mice (in vivo efficacy) that is comparable to that of leuprolide. Testosterone release is an acutely dose dependent effect that is blocked by the LHRH-I receptor antagonist, cetrorelix. The pharmacokinetic advantages and efficacy of cyclo(1-10)[Pro(1), D-Leu(6), BABA(10)] LHRH render this analogue a promising platform for future rational drug design studies towards the development of non-peptide LHRH mimetics.

Conformational analysis of the ΜΒΡ83-99 (Phe91) and ΜΒΡ83-99 (Tyr91) peptide analogues and study of their interactions with the HLA-DR2 and human TCR receptors by using molecular dynamics

The two new synthetic analogues of the MBP(83-99) epitope substituted at Lys(91) (primary TCR contact) with Phe [MBP(83-99) (Phe(91))] or Tyr [MBP(83-99) (Tyr(91))], have been structurally elucidated using 1D and 2D high resolution NMR studies. The conformational analysis of the two altered peptide ligands (APLs) has been performed and showed that they adopt a linear and extended conformation which is in agreement with the structural requirements of the peptides that interact with the HLA-DR2 and TCR receptors. In addition, Molecular Dynamics (MD) simulations of the two analogues in complex with HLA-DR2 (DRA, DRB1*1501) and TCR were performed. Similarities and differences of the binding motif of the two analogues were observed which provide a possible explanation of their biological activity. Their differences in the binding mode in comparison with the MBP(83-99) epitope may also explain their antagonistic versus agonistic activity. The obtained results clearly indicate that substitutions in crucial amino acids (TCR contacts) in combination with the specific conformational characteristics of the MBP(83-99) immunodominant epitope lead to an alteration of their biological activity. These results make the rational drug design intriguing since the biological activity is very sensitive to the substitution and conformation of the mutated MBP epitopes.

Altered peptide ligands of myelin basic protein ( MBP87-99 ) conjugated to reduced mannan modulate immune responses in mice

Mutations of peptides to generate altered peptide ligands, capable of switching immune responses from T helper 1 (Th1) to T helper 2 (Th2), are promising candidates for the immunotherapy of autoimmune diseases such as multiple sclerosis (MS). We synthesized two mutant peptides from myelin basic protein 87-99 (MBP(87-99)), an immunodominant peptide epitope identified in MS. Mutations of residues K(91) and P(96), known to be critical T-cell receptor (TCR) contact sites, resulted in the mutant peptides [R(91), A(96)]MBP(87-99) and [A(91), A(96)]MBP(87-99). Immunization of mice with these altered peptide ligands emulsified in complete Freund's adjuvant induced both interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) responses compared with only IFN-gamma responses induced to the native MBP(87-99) peptide. It was of interest that [R(91), A(96)]MBP(87-99) conjugated to reduced mannan induced 70% less IFN-gamma compared with the native MBP(87-99) peptide. However, [A(91), A(96)]MBP(87-99) conjugated to reduced mannan did not induce IFN-gamma-secreting T cells, but elicited very high levels of interleukin-4 (IL-4). Furthermore, antibodies generated to [A(91), A(96)]MBP(87-99) peptide conjugated to reduced mannan did not cross-react with the native MBP(87-99) peptide. By molecular modelling of the mutant peptides in complex with major histocompatibility complex (MHC) class II, I-A(s), novel interactions were noted. It is clear that the double-mutant peptide analogue [A(91), A(96)]MBP(87-99) conjugated to reduced mannan is able to divert immune responses from Th1 to Th2 and is a promising mutant peptide analogue for use in studies investigating potential treatments for MS.

Neuronal I kappa B kinase beta protects mice from autoimmune encephalomyelitis by mediating neuroprotective and immunosuppressive effects in the central nervous system

Some aspects of CNS-directed autoimmunity in multiple sclerosis are modeled in mice by immunization with myelin Ags where tissue damage is driven by myelin-reactive Th1 and Th17 effector lymphocytes. Whether the CNS plays an active role in controlling such autoimmune diseases is unknown. We used mice in which IkappaB kinase beta was deleted from Ca(2+)/calmodulin-dependent kinase IIalpha-expressing neurons (nIKKbetaKO) to investigate the contribution of neuronal NF-kappaB to the development of myelin oligodendrocyte glycoprotein 35-55-induced experimental autoimmune encephalomyelitis. We show that nIKKbetaKO mice developed a severe, nonresolving disease with increased axon loss compared with controls and this was associated with significantly reduced CNS production of neuroprotective factors (vascular endothelial growth factor, CSF1-R, and FLIP) and increased production of proinflammatory cytokines (IL-6, TNF, IL-12, IL-17, and CD30L) and chemokines. The isolation of CNS-infiltrating monocytes revealed greater numbers of CD4(+) T cells, reduced numbers of NK1.1(+) cells, and a selective accumulation of Th1 cells in nIKKbetaKO CNS from early in the disease. Our results show that neurons play an important role in determining the quality and outcome of CNS immune responses, specifically that neuronal IkappaB kinase beta is required for neuroprotection, suppression of inflammation, limitation of Th1 lymphocyte accumulation, and enhancement of NK cell recruitment in experimental autoimmune encephalomyelitis-affected CNS and stress the importance of neuroprotective strategies for the treatment of multiple sclerosis.

NMR structural elucidation of myelin basic protein epitope 83-99 implicated in multiple sclerosis

Myelin basic protein peptide 83-99 (MBP83-99) is the most immunodominant epitope playing a significant role in the multiple sclerosis (MS), an autoimmune disease of the central nervous system. Many peptide analogues, linear or cyclic have been designed and synthesized based on this segment in order to inhibit the experimental autoimmune encephalomyelitis, the best well-known animal model of MS. In this study, the solution structural motif of MBP(83-99) has been performed using 2D (1)H-NMR spectroscopy in dimethyl sulfoxide. A rather extended conformation, along with the formation of a well defined alpha-helix spanning residues Val(87)-Phe(90) is proposed, as no long-range NOE are presented. Moreover, the residues of MBP peptide that are important for T-cell receptor recognition are solvent exposed. The spatial arrangement of the side chain all over the sequence of our NMR based model exhibits great similarity with the solid state model, while both TCR contacts occupy the same region in space.

Design and synthesis of a cyclic double mutant peptide (cyclo(87-99)[A91,A96]MBP87-99) induces altered responses in mice after conjugation to mannan: implications in the immunotherapy of multiple sclerosis

Altered peptide ligands that alter immune responses are a promising approach to the immunotherapy of multiple sclerosis. Cyclic peptides are of interest because the limited stability of linear peptides restricts their use in vivo. We designed and synthesized a cyclic double mutant peptide from MBP(87-99)-[cyclo(87-99)[A(91),A(96)]MBP(87-99)]. Immunization of mice, in CFA reduced Th1 responses. However, when conjugated to reduced mannan, a significant further reduction of Th1 responses and moderate Th2 responses were induced.

The good, the bad and the ugly: how altered peptide ligands modulate immunity

BACKGROUND

The basis of T cell immune responses is the specific recognition of an immunogenic peptide epitope by a T cell receptor. Peptide alterations of such T cell epitopes with single or few amino acid variations can have drastic effects on the outcome of this recognition. These altered peptide ligands can act as modulators of immune responses as they are capable of downregulating or upregulating responses.

OBJECTIVE/METHODS

We review how altered peptide ligands can have 'good' 'bad' and 'ugly' outcomes in treating diseases.

RESULTS/CONCLUSION

Altered peptide ligands have been used as immunotherapeutics in autoimmune (and allergic) diseases, infectious diseases and cancer. In the next five years we anticipate seeing a number of altered peptide ligands in clinical trials, progressing from contradictory classifications of good, bad or ugly, to the exciting outcome of 'useful'.

Towards immunotherapeutic drugs and vaccines against multiple sclerosis

Multiple sclerosis (MS) is an autoimmune, demyelinating disease of the central nervous system. Numerous treatment options are available to MS patients; however, these options need to be improved. Herein, we review the current drugs and therapeutic approaches available to MS patients, preclinical trial interventions and recent animal model studies for the potential therapy of MS. Since the current treatment of MS remains elusive and is limited, animal studies and clinical research offers an optimistic outlook.

Cyclic and dimeric gluten peptide analogues inhibiting DQ2-mediated antigen presentation in celiac disease

Celiac disease is an immune mediated enteropathy elicited by gluten ingestion. The disorder has a strong association with HLA-DQ2. This HLA molecule is involved in the disease pathogenesis by presenting gluten peptides to T cells. Blocking the peptide-binding site of DQ2 may be a way to treat celiac disease. In this study, two types of peptide analogues, modeled after natural gluten antigens, were studied as DQ2 blockers. (a) Cyclic peptides. Cyclic peptides containing the DQ2-alphaI gliadin epitope LQPFPQPELPY were synthesized with flanking cysteine residues introduced and subsequently crosslinked via a disulfide bond. Alternatively, cyclic peptides were prepared with stable polyethylene glycol bridges across internal lysine residues of modified antigenic peptides such as KQPFPEKELPY and LQLQPFPQPEKPYPQPEKPY. The effect of cyclization as well as the length of the spacer in the cyclic peptides on DQ2 binding and T cell recognition was analyzed. Inhibition of peptide-DQ2 recognition by the T cell receptor was observed in T cell proliferation assays. (b) Dimeric peptides. Previously we developed a new type of peptide blocker with much enhanced affinity for DQ2 by dimerizing LQLQPFPQPEKPYPQPELPY through the lysine side chains. Herein, the effect of linker length on both DQ2 binding and T cell inhibition was investigated. One dimeric peptide analogue with an intermediate linker length was found to be especially effective at inhibiting DQ2 mediated antigen presentation. The implications of these findings for the treatment of celiac disease are discussed.

Comparison of Proposed Putative Active Conformations of Myelin Basic Protein Epitope 87−99 Linear Altered Peptide Ligands by Spectroscopic and Modelling Studies: The Role of Positions 91 and 96 in T-Cell Receptor Activation

This work proposes a structural motif for the inhibition of experimental autoimmune encephalomyelitis (EAE) by the linear altered peptide ligands (APLs) [Ala91,96] MBP87-99 and [Arg91,Ala96] MBP87-99 of myelin basic protein. Molecular dynamics was applied to reveal distinct populations of EAE antagonist [Ala91,96] MBP87-99 in solution, in agreement with NOE data. The combination of the theoretical and experimental results led to the identification of a putative active conformation. This approach is of value as no crystallographic data is available for the APL-receptor complex. TCR contact residue Phe89 has an altered topology in the putative bioactive conformations of both APLs with respect to the native peptide, as found via crystallography; it is no longer prominent and solvent exposed. It is proposed that the antagonistic activity of the APLs is due to their binding to MHC, preventing the binding of self-myelin epitopes, with the absence of an immunologic response as the loss of some interactions with the TCR hinders activation of T-cells.

A putative bioactive conformation for the altered peptide ligand of myelin basic protein and inhibitor of experimental autoimmune encephalomyelitis [Arg91, Ala96] MBP87–99

[Arg(91), Ala(96)] MBP(87-99) is an altered peptide ligand (APL) of myelin basic protein (MBP), shown to actively inhibit experimental autoimmune encephalomyelitis (EAE), which is studied as a model of multiple sclerosis (MS). The APL has been rationally designed by substituting two of the critical residues for recognition by the T-cell receptor. A conformational analysis of the APL has been sought using a combination of 2D NOESY nuclear magnetic resonance (NMR) experiments and detailed molecular dynamics (MD) calculations, in order to comprehend the stereoelectronic requirements for antagonistic activity, and to propose a putative bioactive conformation based on spatial proximities of the native peptide in the crystal structure. The proposed structure presents backbone similarity with the native peptide especially at the N-terminus, which is important for major histocompatibility complex (MHC) binding. Primary (Val(87), Phe(90)) and secondary (Asn(92), Ile(93), Thr(95)) MHC anchors occupy the same region in space, whereas T-cell receptor (TCR) contacts (His(88), Phe(89)) have different orientation between the two structures. A possible explanation, thus, of the antagonistic activity of the APL is that it binds to MHC, preventing the binding of myelin epitopes, but it fails to activate the TCR and hence to trigger the immunologic response. NMR experiments coupled with theoretical calculations are found to be in agreement with X-ray crystallography data and open an avenue for the design and synthesis of novel peptide restricted analogues as well as peptide mimetics that rises as an ultimate goal.

Solution NMR structure of an immunodominant epitope of myelin basic protein. Conformational dependence on environment of an intrinsically unstructured protein

Using solution NMR spectroscopy, three-dimensional structures have been obtained for an 18-residue synthetic polypeptide fragment of 18.5 kDa myelin basic protein (MBP, human residues Q81-T98) under three conditions emulating the protein's natural environment in the myelin membrane to varying degrees: (a) an aqueous solution (100 mM KCl pH 6.5), (b) a mixture of trifluoroethanol (TFE-d2) and water (30 : 70% v/v), and (c) a dispersion of 100 mM dodecylphosphocholine (DPC-d38, 1 : 100 protein/lipid molar ratio) micelles. This polypeptide sequence is highly conserved in MBP from mammals, amphibians, and birds, and comprises a major immunodominant epitope (human residues N83-T92) in the autoimmune disease multiple sclerosis. In the polypeptide fragment, this epitope forms a stable, amphipathic, alpha helix under organic and membrane-mimetic conditions, but has only a partially helical conformation in aqueous solution. These results are consistent with recent molecular dynamics simulations that showed this segment to have a propensity to form a transient alpha helix in aqueous solution, and with electron paramagnetic resonance (EPR) experiments that suggested a alpha-helical structure when bound to a membrane [I. R. Bates, J. B. Feix, J. M. Boggs & G. Harauz (2004) J Biol Chem, 279, 5757-5764]. The high sensitivity of the epitope structure to its environment is characteristic of intrinsically unstructured proteins, like MBP, and reflects its association with diverse ligands such as lipids and other proteins.

Synthesis and study of the electrophoretic behavior of mannan conjugates with cyclic peptide analogue of myelin basic protein using lysine-glycine linker

New approaches for the treatment of multiple sclerosis involve the design and synthesis of peptide or nonpeptide analogues of myelin sheath, which could alter the immune response of patients. For this purpose, the cyclo(75-82) myelin basic protein (MBP)(74-85) analogue was conjugated to mannan (a polymannose) via (Lys-Gly)(5) linker. Monitoring of synthesis of the (Lys-Gly)(5)-containing cyclic analogue of MBP, mannan oxidation, and the conjugation reaction of this analogue to oxidized mannan was performed with capillary electrophoresis (CE) in operating buffers of different pH values. The (Lys-Gly)(5)cyclo(75-82)MBP(74-85) was efficiently synthesized by solid-phase synthesis and purified to a high degree, as confirmed by CE analysis in a low-pH (3.0) phosphate buffer and normal polarity. Oxidation of mannan was monitored using a high-pH (9.3) borate buffer, and the generation of heterogeneous products and even UV-absorbing peaks was shown by CE. CE analysis in a pH 5.1 phosphate buffer offers high resolution of oxidized mannan and the conjugation product and can be used for screening of the reaction products. Mannan-peptide conjugates of varying degrees of substitution and unreacted mannan were observed. The developed CE analysis presents distinct advantages over sodium dodecyl sulfate-polyacrylamide gel electrophoresis such as high versatility, high separation efficiency, short analysis time, low cost, and low solvent consumption.

NMR and molecular dynamics studies of an autoimmune myelin basic protein peptide and its antagonist: structural implications for the MHC II (I-Au)-peptide complex from docking calculations

Experimental autoimmune encephalomyelitis can be induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP). To characterize the molecular features of antigenic sites important for designing experimental autoimmune encephalomyelitis suppressing molecules, we report structural studies, based on NMR experimental data in conjunction with molecular dynamic simulations, of the potent linear dodecapeptide epitope of guinea pig MBP, Gln74-Lys75-Ser76-Gln77-Arg78-Ser79-Gln80-Asp81-Glu82-Asn83-Pro84-Val85 [MBP(74-85)], and its antagonist analogue Ala81MBP(74-85). The two peptides were studied in both water and Me(2)SO in order to mimic solvent-dependent structural changes in MBP. The agonist MBP(74-85) adopts a compact conformation because of electrostatic interactions of Arg78 with the side chains of Asp81 and Glu82. Arg78 is 'locked' in a well-defined conformation, perpendicular to the peptide backbone which is practically solvent independent. These electrostatic interactions are, however, absent from the antagonist Ala81MBP(74-85), resulting in great flexibility of the side chain of Arg78. Sequence alignment of the two analogues with several species of MBP suggests a critical role for the positively charged residue Arg78, firstly, in the stabilization of the local microdomains (epitopes) of the integral protein, and secondly, in a number of post-translational modifications relevant to multiple sclerosis, such as the conversion of charged arginine residues to uncharged citrullines. Flexible docking calculations on the binding of the MBP(74-85) antigen to the MHC class II receptor site I-A(u) using haddock indicate that Gln74, Ser76 and Ser79 are MHC II anchor residues. Lys75, Arg78 and Asp81 are prominent, solvent-exposed residues and, thus, may be of importance in the formation of the trimolecular T-cell receptor-MBP(74-85)-MHC II complex.