CRYSTAL-STRUCTURE OF MOUSE H2-M

H2-M (HLA-DM in humans) resides in an acidic endosomal compartment, wh ere it facilitates the loading of antigenic peptides into the peptide- binding groove of class II MHC. The crystal structure of a soluble for m of H2-M has been solved to 3.1 Angstrom resolution, revealing a hete rodimer with structural similarities to the MHC family of proteins. In contrast to its antigen-presenting cousins, the membrane distal alpha helices of H2-M pack closely together, occluding most of the binding groove except for a single large pocket near the center. The structure of H2-M has several unique features that may play a role in its funct ion as a molecular chaperone and peptide exchange factor.