Substrate selection by transporters associated with antigen processing occurs during peptide binding to TAP

Area of Science:

• Immunology
• Molecular Biology
• Protein Transport

Background:

• Major histocompatibility complex (MHC) class I molecules present antigenic peptides, a process reliant on peptide translocation into the endoplasmic reticulum (ER) by transporters associated with antigen processing (TAP).
• TAP-mediated peptide transport involves peptide binding and ATP-dependent translocation, with previous studies indicating allele- and species-specific variations in transport efficiency based on peptide C-termini.

Purpose of the Study:

• To determine at which step of interaction with TAP peptide selection occurs.
• To investigate the binding affinity of various peptides to human and rat TAP complexes.
• To elucidate the role of peptide C-termini in TAP binding selectivity.

Main Methods:

• Utilized a peptide binding assay to assess the binding affinity of 199 peptides to human TAP and two allelic rat TAP complexes.
• Analyzed the influence of peptide C-terminal residues on binding affinity across different TAP transporters.

Main Results:

• A dominant influence of the peptide C-terminus on binding affinity was observed for all tested TAP transporters.
• Rat TAP1/TAP2u complexes exhibited highly restrictive selection of peptides with aliphatic and aromatic C-termini.
• The observed peptide binding selectivity aligns with established data on rat TAP-mediated peptide transport and antigen presentation.

Conclusions:

• Peptide selection by TAP exclusively occurs during the initial peptide binding step.
• All molecular factors governing peptide selection by TAP are present in insect cells, suggesting their suitability for further study.