1R5I: Crystal Structure Of The Mam-Mhc Complex

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.
PDB ID: 1R5IDownload
MMDB ID: 26898
PDB Deposition Date: 2003/10/10
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2.6  Å
Source Organism:
synthetic construct
Similar Structures:
Biological Unit for 1R5I: tetrameric; determined by author
Molecular Components in 1R5I
Label Count Molecule
Proteins (4 molecules)
HLA Class II Histocompatibility Antigen, DR Alpha Chain(Gene symbol: HLA-DRA)
Molecule annotation
HLA Class II Histocompatibility Antigen, Drb1-1 Beta Chain(Gene symbol: HLA-DRB1)
Molecule annotation
Hemagglutinin Peptide
Molecule annotation
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB