3-DIMENSIONAL STRUCTURE OF THE HUMAN CLASS-II HISTOCOMPATIBILITY ANTIGEN HLA-DR1

The three-dimensional structure of the class II histocompatibility gly coprotein HLA-DR1 from human B-cell membranes has been determined by X -ray crystallography and is similar to that of class I HLA. Peptides a re bound in an extended conformation that projects from both ends of a n 'open-ended' antigen-binding groove. A prominent non-polar pocket in to which an 'anchoring' peptide side chain fits is near one end of the binding groove. A dimer of the class II alphabeta heterodimers is see n in the crystal forms of HLA-DR1, suggesting class II HLA dimerizatio n as a mechanism for initiating the cytoplasmic signalling events in T -cell activation.