Molecular dynamics at the receptor level of immunodominant myelin basic protein epitope 87-99 implicated in multiple sclerosis and its antagonists altered peptide ligands: Triggering of immune response

This work reports molecular dynamics studies at the receptor level of the immunodominant myelin basic protein (MBP) epitope 87–99 implicated in multiple sclerosis, and its antagonists altered peptide ligands (APLs), namely [Arg91, Ala96] MBP87–99 and [Ala91,96] MBP87–99. The interaction of each peptide ligand with the receptor human leukocyte antigen HLA-DR2b was studied, starting from X-ray structure with pdb code: 1ymm. This is the first such study of APL-HLA-DR2b complexes, and hence the first attempt to gain a better understanding of the molecular recognition mechanisms that underlie TCR antagonism by these APLs. The amino acids His88 and Phe89 serve as T-cell receptor (TCR) anchors in the formation of the trimolecular complex TCR-peptide-HLA-DR2b, where the TCR binds in a diagonal, off-centered mode to the peptide-HLA complex. The present findings indicate that these two amino acids have a different orientation in the APLs [Arg91, Ala96] MBP87–99 and [Ala91,96] MBP87–99: His88 and Phe89 remain buried in HLA grooves and are not available for interaction with the TCR. We propose that this different topology could provide a possible mechanism of action for TCR antagonism

A combined NMR and molecular dynamics simulation study to determine the conformational properties of agonists and antagonists against experimental autoimmune encephalomyelitis

Myelin basic protein (MBP) is one of the best characterized autoantigens causing multiple sclerosis (MS), via a procedure that involves a stable formation of the trimolecular complex of a T-cell Receptor (TCR), an MBP epitope, and the receptor HLA-DR2b. Experimental autoimmune encephalomyelitis (EAE) is considered as an instructive model for MS in humans, and plenty of X-ray data is available for a number of EAE inducing peptide-receptor complexes. To date, though, there are no data available for complexes involving peptides reversing EAE, namely antagonists. Conformational properties of the EAE inducing epitope MBP87–99 were analyzed in DMSO using the NOE connectivities and vicinal HN–Hα coupling constants, and compared with the antagonist altered peptide ligands. A robust method, which is based on a combination of molecular dynamics and energy minimization, is proposed for identifying the putative bioactive conformations. Generated conformations are compared with the known X-ray structure of MBP83–96 (human sequence numbering) in the HLA-DR2b complex. The structural motif for the agonist–antagonist activity is discussed

Putative bioactive conformations of amide linked cyclic myelin basic protein peptide analogues associated with experimental autoimmune encephalomyelitis

The solution models of cyclo(87−99) MBP87-99, cyclo(87−99) [Ala91,96] MBP87-99, and cyclo(87−99) [Arg91, Ala96] MBP87-99 have been determined through 2D NMR spectroscopy in DMSO-d6. Chemical shift analysis has been performed in an attempt to elucidate structural changes occurring upon substitution of native residues. NMR-derived geometrical constraints have been used in order to calculate high-resolution conformers of the above peptides. Conformational analysis of the three synthetic analogues show that the bioactivity, or the lack of it, may possibly be due to the distinct local structure observed and the subsequent differences in the overall topology and exposed area after binding with Major Histocompatibility Complex II (MHC II). It is believed that an overall larger solvent accessible area blocks the approach and binding of the T-cell receptor (TCR) on the altered peptide ligand (APL)−MHC complex, whereas more compact structures do not occlude weak interactions with an approaching TCR and can cause Experimental Autoimmune Encephalomyelitis (EAE) antagonism. A pharmacophore model based on the structural data has been generated

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 combined NMR and molecular dynamics simulation study to determine the conformational properties of rat/mouse 35-55 myelin oligodendrocyte glycoprotein epitope implicated in the induction of experimental autoimmune encephalomyelitis

A combined NMR and molecular dynamics simulation study to determine the conformational properties of rat/mouse 35-55 myelin oligodendrocyte glycoprotein epitope implicated in the induction of experimental autoimmune encephalomyeliti