STRUCTURE OF THE MHC CLASS II MOLECULE HLA-DR4/HA306-318 PEPTIDE/ SUPERANTIGEN COMPLEX. W.C. Stallings, A.M. Stevens, R.A. Stegeman, M.L. Zacheis, D.A. Kirschmann, T. Witman, X-T. Fu, R.F. Karr, B.D. Schwartz, and S.L. Woulfe, Monsanto-Searle, 700 Chesterfield Village Parkway, St. Louis, MO 63198 USA

The crystal structure of a rheumatoid arthritis-associated human leukocyte antigen DR4 Dw4 complexed with the superantigen, S. aureus enterotoxin B, has been solved by molecular replacement techniques at 2.8 resolution (1). The peptide binding groove was loaded with a 13-residue antigenic peptide from hemagglutinin, HA306-318. Comparison of the DR1 (2) and DR4 peptide binding domains with bound HA306-318 revealed differences in the DR1 and DR4 backbones in the N-terminus of the a-chain helix beginning near residue 51 and continuing through residue 74 with maximal displacement between the two structures near the C-terminus of this region. In general, many of the DR1-HA peptide interactions were preserved in the DR4-HA structure. There were, however, significant differences in the orientation of peptide side chains at Lys 310, Gln 311, Asn 312, Lys 315, and Leu 316. Thus, the different class II major histocompatibility complex molecules recognize the same peptide in different ways. These findings provide support for the hypothesis that the orientation of peptide in the groove influences T cell recognition.

Crystals were grown from polyethylene glycol over a considerable pH range. The lattice parameters are a = 91.5, b =92.5, c =102.3 , space group P212121 with a single superantigen and peptide-loaded MHC Class II molecule in the asymmetric unit; thus DR4 does not crystallize as a dimer. Data, 75% complete, were collected from a single crystal flashed cooled in a liquid nitrogen stream.

1. TS Jardetzky, JH Brown, JC Gorga, LJ Stern, RG Urban, Y-I Chi, C Stauffacher, JL Strominger & DC Wiley (1994) Nature 368, 711.

2. LJ Stern, JH Brown, TJ Jardetzky, JC Gorga, RG Urban, JL Stromeyer & DC Wiley (1993) Nature 368, 215.