pH-dependent peptide binding properties of the type I diabetes-associated I-Ag7 molecule: rapid release of CLIP at an endosomal pH.
MHC class II molecules and invariant chain assemble at a neutral pH in the endoplasmic reticulum and are transported to a low pH compartment where the invariant chain is trimmed to the class II-associated invariant chain peptide (CLIP). For many major histocompatibility complex class II molecules, DM is required for rapid removal of CLIP, which allows binding of antigenic peptides. Since I-Ag7 confers susceptibility to type I diabetes in NOD mice, the biochemical requirements for peptide loading were examined using soluble I-Ag7 expressed in insect cells. I-Ag7 formed long-lived complexes with naturally processed peptides from transferrin and albumin, whereas several peptides that represent T cell epitopes of islet autoantigens were poor binders. I-Ag7-peptide complexes were not sodium dodecyl sulfate (SDS) resistant, indicating that SDS sensitivity may be an intrinsic property of I-Ag7. Complexes of I-Ag7 and CLIP formed at a neutral pH, but rapidly dissociated at pH 5. This rapid dissociation was due to a poor fit of M98 of CLIP in the P9 pocket of I-Ag7, since substitution of M98 by a negatively charged residue greatly enhanced the stability of the complex. These biochemical properties of I-Ag7 result in the rapid generation of empty molecules at an endosomal pH and have a global effect on peptide binding by I-Ag7.
Hausmann
D H
DH
Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
Yu
B
B
Hausmann
S
S
Wucherpfennig
K W
KW
D000595:Amino Acid Sequence; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D004331:Drosophila melanogaster; D011992:Endosomes / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D000944:Antigens, Differentiation, B-Lymphocyte; D017931:DNA Primers; D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D010455:Peptides; D011994:Recombinant Proteins; C045084:invariant chain