How a T cell receptor-like antibody recognizes major histocompatibility complex-bound peptide

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• T cell receptors (TCRs) recognize peptide-MHC complexes, initiating adaptive immune responses.
• TCR-like antibodies are engineered to mimic TCR recognition but can exhibit distinct binding properties.
• Understanding these binding mechanisms is crucial for developing targeted immunotherapies.

Purpose of the Study:

• To elucidate the structural basis of TCR-like antibody recognition of peptide-MHC complexes.
• To compare the binding modes of different TCR-like antibodies.
• To identify distinct mechanisms by which antibodies can interact with peptide-MHC antigens.

Main Methods:

• Determined crystal structures of the 25-D1.16 Fab fragment bound to H-2K(b)-SIINFEKL complex.
• Analyzed the binding orientation and interactions of the antibody with the peptide-MHC.
• Compared these structures with previously determined structures of other TCR-like antibodies (e.g., Hyb3).

Main Results:

• The 25-D1.16 antibody binds peptide-MHC in a canonical diagonal orientation, similar to most TCRs.
• This antibody directly recognizes the structure of the MHC-bound peptide.
• In contrast, the Hyb3 antibody exhibits a non-canonical orientation and recognizes a conformational epitope where the MHC is dominant.

Conclusions:

• TCR-like antibodies can employ at least two distinct mechanisms to recognize MHC-bound peptides.
• One mechanism mimics the canonical TCR binding mode.
• The other mechanism involves a non-canonical antibody orientation, highlighting the versatility of antibody recognition strategies.