Crystallization of HLA-DR antigens

The class II major histocompatibility antigens HLA-DR1, DR2, DR3, DR4, DR7 and DR8 were purified by immunoaffinity chromatography from homozygous human B lymphoblastoid cell lines. The purified, detergent-soluble molecules were cleaved with the protease papain to remove the hydrophobic transmembrane regions and cytoplasmic tails. Crystals were obtained for each of the papain-solubilized fragments. DR1 crystallized under a variety of different conditions, resulting in two different orthorhombic crystal forms, one of which diffracts as far as 3.5A. Crystals of DR2, DR3, DR4 and DR8 have the same unit cell dimensions as the DR1 crystals, and crystals of DR3 and DR4 have the same diffracting power as the DR1 crystals. The best DR7 crystals obtained thus far are hexagonal and diffract to only about 8A. Crystals of similar hexagonal form have also been observed for most of the other DR subsets.