DM loss in k haplotype mice reveals isotype-specific chaperone requirements.
DM actions as a class II chaperone promote capture of diverse peptides inside the endocytic compartment(s). DM mutant cells studied to date express class II bound by class II-associated invariant chain-derived peptide (CLIP), a short proteolytic fragment of the invariant chain, and exhibit defective peptide-loading abilities. To evaluate DM functional contributions in k haplotype mice, we engineered a novel mutation at the DMa locus via embryonic stem cell technology. The present experiments demonstrate short-lived A(k)/CLIP complexes, decreased A(k) surface expression, and enhanced A(k) peptide binding activities. Thus, we conclude that DM loss in k haplotype mice creates a substantial pool of empty or loosely occupied A(k) conformers. On the other hand, the mutation hardly affects E(k) activities. The appearance of mature compact E(k) dimers, near normal surface expression, and efficient Ag presentation capabilities strengthen the evidence for isotype-specific DM requirements. In contrast to DM mutants described previously, partial occupancy by wild-type ligands is sufficient to eliminate antiself reactivity. Mass spectrometry profiles reveal A(k)/CLIP and a heterogeneous collection of relatively short peptides bound to E(k) molecules. These experiments demonstrate that DM has distinct roles depending on its specific class II partners.
Koonce
Chad H
CH
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Wutz
Gordana
G
Robertson
Elizabeth J
EJ
Vogt
Anne B
AB
Kropshofer
Harald
H
Bikoff
Elizabeth K
EK
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D003433:Crosses, Genetic; D005260:Female; D017353:Gene Deletion; D006183:H-2 Antigens / Q000235:genetics; D006239:Haplotypes; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000145:classification / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D018832:Molecular Chaperones / Q000145:classification / Q000502:physiology*; D008969:Molecular Sequence Data; D009113:Muramidase / Q000276:immunology / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017393:RNA Editing / Q000276:immunology; D017634:Self Tolerance / Q000235:genetics
D000944:Antigens, Differentiation, B-Lymphocyte; D006183:H-2 Antigens; C024755:H-2K(K) antigen; C416189:H2-M antigens; D000949:Histocompatibility Antigens Class II; C111388:I-Ak antigen; C024138:I-E-antigen; D018832:Molecular Chaperones; D010446:Peptide Fragments; C045084:invariant chain; C066759:hen egg lysozyme peptide (46-61); D009113:Muramidase