Macromolecular Modeling Blog ™

Although numerous structures of peptide bound MHC-II molecules were solved, no one knows how does the peptide free MHC look like. Painter et al. elegantly use molecular dynamics to model the conformational changes upon peptide removal. Most interestingly a helix from the peptide binding domain adopts the binding mode of the antigen peptide. They successfully validate their model using antibodies and superantigens, predicted to differentially bind peptide-bound/free molecules according to their model. We take the validation one step further and propose mutations based on Painter’s model that would stabilize the free MHC. Will it work? Who will pick up the gauntlet?

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Carlos J. Camacho et al. study the relationship between peptide stabilities and their immunogenicity. They present a model system of several peptides corresponding to portions of murine HRS which are capable of inducing anti-protein antibodies of varying affinity and temporal persistence. On this system they show by molecular dynamics simulations, that sequences of the most immunogenic peptides correspond to highly ordered structural motifs in the parent protein. Competitive ELISAs provide direct evidence that these peptides share structural determinants with native protein. More interestingly they address the question of how can these less stable peptides induce the same immunogenic response. By Nir London

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