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Ashman JB, Miller J. A Role for the Transmembrane Domain in the Trimerization of the MHC Class II-Associated Invariant Chain. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.163.5.2704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
MHC class II and invariant chain (Ii) associate early in biosynthesis to form a nonameric complex. Ii first assembles into a trimer and then associates with three class II αβ heterodimers. Although the membrane-proximal region of the Ii luminal domain is structurally disordered, the C-terminal segment of the luminal domain is largely α-helical and contains a major interaction site for the Ii trimer. In this study, we show that the Ii transmembrane domain plays an important role in the formation of Ii trimers. The Ii transmembrane domain contains an unusual patch of hydrophilic residues near the luminal interface. Substitution of these polar residues with nonpolar amino acids resulted in a decrease in the efficiency of Ii trimerization and subsequent class II association. Moreover, N-terminal fragments of Ii were found to trimerize independently of the luminal α-helical domain. Progressive C-terminal truncations mapped a homotypic association site to the first 80 aa of Ii. Together, these results implicate the Ii transmembrane domain as a site of trimer interaction that can play an important role in the initiation of trimer formation.
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Affiliation(s)
| | - Jim Miller
- *Committee on Immunology and
- †Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
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Bikoff EK, Kenty G, Van Kaer L. Distinct Peptide Loading Pathways for MHC Class II Molecules Associated with Alternative Ii Chain Isoforms. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.7.3101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
Mutant mouse strains expressing either p31 or p41 Ii chain appear equally competent with respect to their class II functional activities including Ag presentation and CD4+ T cell development. To further explore possibly divergent roles provided by alternative Ii chain isoforms, we compare class II structure and function in double mutants also carrying a null allele at the H2-DM locus. As for DM mutants expressing wild-type Ii chain, AαbAβb dimers present in DM-deficient mice expressing either Ii chain isoform appear equally occupied by class II-associated Ii chain-derived peptides (CLIP). Surprisingly, in functional assays, these novel mouse strains exhibit strikingly different phenotypes. Thus, DM-deficient mice expressing wild-type Ii chain or p31 alone are both severely compromised in their abilities to present peptides. In contrast, double mutants expressing the p41 isoform display markedly enhanced peptide-loading capabilities, approaching those observed for wild-type mice. The present data strengthen evidence for divergent class II presentation pathways and demonstrate for the first time that functionally distinct roles are mediated by alternatively spliced forms of the MHC class II-associated Ii chain in a physiologic setting.
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Affiliation(s)
- Elizabeth K. Bikoff
- *Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, MA 02138; and
| | - George Kenty
- *Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, MA 02138; and
| | - Luc Van Kaer
- †Howard Hughes Medical Institute, Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232
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