PDB 1R5I deposited: 2003-10-10 modified: 2009-02-24
Title Crystal structure of the MAM-MHC complex
Authors Drozd, S.J., Guo, Y., Li, H., Li, Z., Mourad, W., Zhao, Y.
Structure factors resolution 2.6 rfactor 0.238 rfree 0.246
DPI 0.86 theoretical min: 0.38

Mycoplasma arthritidis-derived mitogen (MAM) is a superantigen that can activate large fractions of T cells bearing particular TCR Vbeta elements. Here we report the crystal structure of MAM complexed with a major histocompatibility complex (MHC) antigen, HLA-DR1, loaded with haemagglutinin peptide 306-318 (HA). The structure reveals that MAM has a novel fold composed of two alpha-helical domains. This fold is entirely different from that of the pyrogenic superantigens, consisting of a beta-grasped motif and a beta barrel. In the complex, the N-terminal domain of MAM binds orthogonally to the MHC alpha1 domain and the bound HA peptide, and to a lesser extent to the MHC beta1 domain. Two MAM molecules form an asymmetric dimer and cross-link two MHC antigens to form a plausible, dimerized MAM-MHC complex. These data provide the first crystallographic evidence that superantigens can dimerize MHC molecules. Based on our structure, a model of the TCR2MAM2MHC2 complex is proposed.

Structure 2004 Feb; 12(2):277-288 doi:10.1016/S0969-2126(04)00020-6

Cross References
Database source Identifier Description
PubMed 14962388 STRUE6
Biomolecule Structure Assembly Serial Assembly Type Conformational State Chains Ligands Atoms
1R5I/1 1R5I 1 tetramer 0 4 2 4739
1R5I/2 1R5I 2 tetramer 0 4 2 4712