| Abstract
| - Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP), such as guinea pig sequence MBP72-85.Two linear and one cyclic analogues based on MBP72-85 have been synthesized and evaluatedfor EAE induction in Lewis rats. The linear peptide Gln-Lys-Ser-Gln-Arg-Ser-Gln-Asp-Glu-Asn-Pro-Val (1) was found to induce EAE, while substitution of the Asp residue atposition 8 with Ala resulted in an analogue (2) which suppressed the induction of EAE by itsparent peptide. Nuclear magnetic resonance studies of analogue 1 in dimethyl sulfoxide (DMSO)using TOCSY/ROESY techniques revealed a head-to-tail intramolecular interaction (ROEconnectivity between βVal12-γGln1), indicating a pseudocyclic conformation for the immunogenicpeptide 1. A conformational model was developed using NMR constraints and moleculardynamics. Based on this model, a novel amide-linked cyclic analogue has been designed andsynthesized by connecting the side-chain amino and carboxyl groups of Lys and Glu at positions2 and 9, respectively, of linear analogue 1. The cyclic analogue (3) had similar activity to the linear peptide 1, and the EAE effectsinduced by cyclic analogue 3 were completely suppressed by co-injection with the Ala81-substituted analogue 2 in Lewis rats. The similar potencies of analogues 1 and 3 support theproposed cyclic comformation suggested for analogue 1 from NMR studies and computermodeling and provides the basis for designing more potent molecules with improved propertiessuch as increased resistance to degradation. The present findings suggest that a cyclicconformation for the MBP72-85 epitope positions the carboxyl group of Asp81 correctly andpresumably other side groups of the peptide such as Arg78 in a manner which enables functionalbinding of the trimolecular complex MHC−peptide−T cell receptor resulting in EAE.
|
