title: Stoichiometry of HLA class II-invariant chain oligomers.
abstract: BACKGROUND
  The HLA gene complex encodes three class II isotypes, DR, DQ, and DP. HLA class II molecules are peptide receptors that present antigens for recognition by T lymphocytes. In antigen presenting cells, the assembly of matched α and β subunits to heterodimers is chaperoned by invariant chain (Ii). Ii forms a homotrimer with three binding sites for class II heterodimers. The current model of class II and Ii structure states that three αβ heterodimers bind to an Ii trimer.
  
  
  RESULTS
  [corrected] We have now analyzed the composition and size of the complexes of class II and Ii using epitope tagged class II subunits and density gradient experiments. We show here that class II-Ii oligomers consist of one class II heterodimer associated with one Ii trimer, such that the DR, DQ and DP isotypes are contained within separate complexes with Ii.
  
  
  CONCLUSIONS
  We propose a structural model of the class II-Ii oligomer and speculate that the pentameric class II-Ii complex is bent towards the cell membrane, inhibiting the binding of additional class II heterodimers to Ii.
authors.affiliation: Division of Immunobiology, Institute of Genetics, University of Bonn, Bonn, Germany. norbert.koch@uni-bonn.de
authors.forename: Norbert
authors.initials: N
authors.lastname: Koch
authors.forename: Martin
authors.initials: M
authors.lastname: Zacharias
authors.forename: Angelika
authors.initials: A
authors.lastname: König
authors.forename: Sebastian
authors.initials: S
authors.lastname: Temme
authors.forename: Jürgen
authors.initials: J
authors.lastname: Neumann
authors.forename: Sebastian
authors.initials: S
authors.lastname: Springer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000938:Antigen-Presenting Cells / Q000737:chemistry / Q000276:immunology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D019556:COS Cells; D002458:Cell Fractionation; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D006681:HLA-D Antigens / Q000032:analysis* / Q000737:chemistry; D006682:HLA-DP Antigens / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D006683:HLA-DQ Antigens / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D006684:HLA-DR Antigens / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D055503:Protein Multimerization / Q000502:physiology*; D020836:Protein Structure, Quaternary; D014461:Ultracentrifugation
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D006681:HLA-D Antigens; D006682:HLA-DP Antigens; D006683:HLA-DQ Antigens; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; C045084:invariant chain