López-Sagaseta J, Kung JE, Savage PB, Gumperz J, Adams EJ. The molecular basis for recognition of CD1d/α-galactosylceramide by a human non-Vα24 T cell receptor.
PLoS Biol 2012;
10:e1001412. [PMID:
23109910 PMCID:
PMC3479090 DOI:
10.1371/journal.pbio.1001412]
[Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 09/12/2012] [Indexed: 11/27/2022] Open
Abstract
Human Vα24− CD1d-restricted T cells use variation in their CDR1α loop to respond to lipid antigens presented by CD1d, altering their specificities from that of invariant natural killer T cells.
CD1d-mediated presentation of glycolipid antigens to T cells is capable of initiating powerful immune responses that can have a beneficial impact on many diseases. Molecular analyses have recently detailed the lipid antigen recognition strategies utilized by the invariant Vα24-Jα18 TCR rearrangements of iNKT cells, which comprise a subset of the human CD1d-restricted T cell population. In contrast, little is known about how lipid antigens are recognized by functionally distinct CD1d-restricted T cells bearing different TCRα chain rearrangements. Here we present crystallographic and biophysical analyses of α-galactosylceramide (α-GalCer) recognition by a human CD1d-restricted TCR that utilizes a Vα3.1-Jα18 rearrangement and displays a more restricted specificity for α-linked glycolipids than that of iNKT TCRs. Despite having sequence divergence in the CDR1α and CDR2α loops, this TCR employs a convergent recognition strategy to engage CD1d/αGalCer, with a binding affinity (∼2 µM) almost identical to that of an iNKT TCR used in this study. The CDR3α loop, similar in sequence to iNKT-TCRs, engages CD1d/αGalCer in a similar position as that seen with iNKT-TCRs, however fewer actual contacts are made. Instead, the CDR1α loop contributes important contacts to CD1d/αGalCer, with an emphasis on the 4′OH of the galactose headgroup. This is consistent with the inability of Vα24− T cells to respond to α-glucosylceramide, which differs from αGalCer in the position of the 4′OH. These data illustrate how fine specificity for a lipid containing α-linked galactose is achieved by a TCR structurally distinct from that of iNKT cells.
Certain lineages of T cells can recognize lipids as stimulatory antigens when presented in the context of CD1 molecules. We know how most Natural Killer T (NKT) cells react with this unusual ligand because they use a single invariant T cell receptor (TCR) alpha chain to do the job. NKT cells place particular emphasis on their CDR3α and CDR2β loops in recognition of antigen—these complementarity determining regions (CDRs) are the hypervariable parts of the TCR that “complement” an antigen's shape. How do these other T cells recognize closely related yet distinct lipid antigens? Here we show that human CD1d-restricted T cells, typically called Vα24− T cells due to their use of diverse Vα domains in their TCRs, use similar molecular strategies to respond to lipid antigens presented by CD1d. To this end we present a 2.5 Å complex structure of a Vα24− TCR complexed with CD1d presenting the protypical lipid, α-galactosylceramide (αGalCer). The TCR examined in this study notably shifts its binding slightly, placing more emphasis on the interaction with the CDR1α loop as revealed through alanine scanning mutagenesis. This shift explains the inability of these T cells to respond to lipids that vary at this site of contact (the 4'OH), like the related α-linked glucosylceramide. These results provide a molecular basis for the fine-specificity of different CD1d-restricted T cell lineages.
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