Ovalbumin(323-339) peptide binds to the major histocompatibility complex class II I-A(d) protein using two...

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Major histocompatibility complex (MHC) class II molecules present antigenic peptides to T cells.
• Previous studies suggested specific residues within the ovalbumin (Ova) 323-339 peptide are crucial for binding to I-A(d) MHC class II.
• Structural data indicated residues 323-324 of the Ova peptide interact with I-A(d), but an alternative binding register was proposed.

Purpose of the Study:

• To investigate the binding of Ova peptides to I-A(d) MHC class II in different registers.
• To determine the impact of specific residue mutations on peptide-MHC binding kinetics.
• To assess the T-cell response to peptides bound in distinct registers.

Main Methods:

• Synthesized and utilized Ova peptides (Ova(323-335) and Ova(325-336)) to study binding to I-A(d).
• Assessed peptide dissociation kinetics from wild-type and mutant I-A(d) (His81 to asparagine substitution).
• Evaluated T-cell hybridoma activation by peptides bound in different registers.

Main Results:

• Ova(323-335) and Ova(325-336) peptides dissociated from I-A(d) with distinct kinetics.
• Replacing His81 in the MHC beta-chain with asparagine enhanced the dissociation rates of both peptides.
• Ova(323-335) binding in one register did not stimulate a T-cell hybridoma, while Ova(325-336) in an alternate register did.

Conclusions:

• A single peptide can bind to an MHC class II molecule in alternate registers.
• These distinct binding modes lead to differential T-cell activation.
• Understanding peptide-MHC binding registers is critical for predicting T-cell responses.