Key residues at third CDR3β position impact structure and antigen recognition of human invariant natural killer T cell receptors

摘要

The human invariant natural killer T (iNKT) TCR is largely composed of the invariant TCR Vα24-Jα18 chain and semi-variant TCR Vβ11 chains with variable CDR3β sequences. The direct role of CDR3β in antigen recognition has been extensively studied. Although it has been noted that CDR3β can interact with CDR3α, how this interaction might indirectly influence antigen recognition is not fully elucidated. We observed that the third position of Vβ11 CDR3 can encode an arginine (Arg) or serine (Ser) residue as a result of somatic rearrangement. Clonotypic analysis of the two iNKT TCR types with a single amino acid substitution revealed that the staining intensity by anti-Vα24 antibodies depends on whether Ser or Arg is encoded. When stained with an anti-Vα24-Jα18 antibody, human primary iNKT cells could be divided into Vα24 low- and high-intensity subsets, and Arg-encoding TCR Vβ11 chains were more frequently isolated from the Vα24 low-intensity compared with the Vα24 high-intensity subpopulation. The Arg/Ser substitution also influenced antigen recognition as determined by CD1d multimer staining and CD1d-restricted functional responses. Importantly, in silico modeling validated that this Ser to Arg mutation could alter the structure of not only the CDR3β but also the CDR3α loop. Collectively, these results indicate that the Arg/Ser encoded at the third CDR3β residue can effectively modulate the overall structure of and antigen recognition by human iNKT TCRs.