Catalyzing Of Immune Peptide/Mhc Class Ii Complex With Dm Molecule Observed By Diffracted X-Ray Tracking (Dxt)

Major Histocompatibility complex (MHC) Class II Molecule has important role on activation of the immune system. Antigen presenting cells engulf extracellular molecules by endocytosis, then the molecules are decomposed into small peptides. MHC class II molecule binds a one of small peptides, then be transported onto the cell surface and present the peptide to T cell receptor to activate the immune system. While MHC class II molecule binds a peptide, it is said that DM molecule which is homolog of MHC class II molecule catalyzes and controls the peptide binding process of MHC class II molecule. But, the detailed information about the control has not been revealed obviously yet.In order to elucidate the mechanism of DM moleculeu0027s catalyzation, we performed Diffracted X-ray Tracking (DXT) to observe motions of peptides bound onto MHC class II molecule with or without DM molecule effects. In DXT, we immobilize proteins on the prepared surface and attach a single gold nanocrystal on a single protein on the surface by using thiol-specific binding. Then, by irradiating pulse x-rays from synchrotron sources, x-rays are diffracted as time-resolvable diffraction spots by gold nanocrystals on proteins. By tracking diffracted spots, we obtain two-dimensional motions of single gold nanocrystal which is related to single moleculeu0027s ones.We observed motions of two types of peptides whose length are different from each other (14 residues and 9 residues) to observe DM moleculeu0027s dependency on a peptide length. Furthermore, we also observed other two peptides whose sequences are slightly modified in order to change a location of labeled nanocrystals. In the poster session, we are going to discuss results from these experiments and MD simulations we are performing.