Human transporters associated with antigen processing possess a promiscuous peptide-binding site

Area of Science:

• Immunology
• Molecular Biology
• Protein Transport

Background:

• The transporters associated with antigen processing (TAP) are crucial for the adaptive immune system.
• TAP facilitates the translocation of antigenic peptides from the cytoplasm to the endoplasmic reticulum for presentation by MHC class I molecules.

Purpose of the Study:

• To investigate the peptide length selectivity of the human TAP complex.
• To identify the optimal peptide size range for TAP-mediated translocation.
• To characterize the peptide-binding properties of TAP.

Main Methods:

• Utilized a panel of peptides with varying lengths and sequences.
• Assayed peptide translocation using a labeled reporter peptide in Streptolysin O (SLO)-permeabilized cells.
• Synthesized a photoactive peptide analogue to photolabel TAP molecules.

Main Results:

• Human TAP exhibits promiscuity for peptides in the 8-12 amino acid range.
• TAP shows increased selectivity and reduced translocation efficiency for peptides between 13-30 amino acids.
• The minimum and maximum effective peptide lengths for TAP translocation are approximately 8 and 25 amino acids, respectively.
• An ATP-independent peptide-binding site on TAP was identified using a photoactive analogue.

Conclusions:

• Peptide length significantly influences human TAP selectivity and translocation efficiency.
• Competition for translocation is directly related to competition for peptide binding to TAP.
• The findings provide insights into the molecular mechanisms of antigen processing and presentation.