Mutations affecting the superantigen activity of staphylococcal enterotoxin B

Area of Science:

• Immunology
• Molecular Biology
• Protein Chemistry

Background:

• Staphylococcal enterotoxin B (SEB) is a superantigen binding to MHC class II and recognized by T cells.
• Previous studies used site-specific mutagenesis to identify residues interacting with the T-cell receptor (TCR) beta-chain.

Purpose of the Study:

• To further define the SEB molecule's face involved in TCR beta-chain interaction.
• To generate and analyze SEB mutants with altered superantigen activity.

Main Methods:

• Polymerase chain reaction (PCR)-based site-specific mutagenesis was employed.
• Amino acid substitutions were generated to assess effects on superantigen activity.
• T-cell proliferation assays and radiolabeled binding analyses were performed.

Main Results:

• Valine at position 169 is critical for SEB function; substitutions here significantly reduced T-cell proliferation.
• Mutant toxins at residue 169 retained TCR V beta selectivity.
• Mutation of histidine at position 166 did not alter SEB superantigen activity or MHC class II binding.

Conclusions:

• SEB residue 169 (valine) is essential for its superantigen activity.
• The interaction with TCR likely involves SEB residues surrounding a cavity on one side of the toxin molecule.
• Histidine 166 is not critical for SEB's superantigen function or MHC class II binding.