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Characteristics of ATP-dependent peptide transport in isolated microsomes

B Yang1, T J Braciale

  • 1Beirne B. Carter Center for Immunology Research, University of Virginia Health Sciences Center, Charlottesville 22908, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|October 15, 1995
PubMed

Insights

The transporter for antigen presentation (TAP) complex efficiently transports peptides, but its rate is influenced by peptide concentration, not competition. Flanking residues also affect peptide transport efficiency.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • The transporter for antigen presentation (TAP) complex is crucial for adaptive immunity.
  • TAP facilitates the transport of antigenic peptides to the endoplasmic reticulum for MHC class I loading.
  • Understanding TAP kinetics and specificity is vital for vaccine development and immunotherapy.

Purpose of the Study:

  • To characterize the transport properties and specificity of the murine TAP complex.
  • To investigate the influence of peptide concentration and flanking residues on TAP-mediated transport.
  • To assess the role of peptide competition in TAP transport and T cell immunodominance.

Main Methods:

  • Utilized isolated microsome preparations from H-2d haplotype mice.
  • Assayed ATP-dependent peptide transport kinetics (Km and Vmax) using a modified influenza nucleoprotein peptide.
  • Examined TAP specificity for various MHC class I binding epitopes and the impact of flanking residues.

Main Results:

  • The murine TAP complex exhibited a high Km (661 nM), indicating substrate concentration influences transport efficiency.
  • Maximum velocity (Vmax) was determined to be 2.9 fmol/min/µg microsome protein.
  • Peptide transport efficiency was affected by flanking residues, suggesting specificity beyond the core epitope.

Conclusions:

  • TAP-mediated peptide transport is sensitive to cytoplasmic peptide concentrations, not primarily driven by inter-peptide competition.
  • The findings suggest that peptide processing and availability, rather than competition for TAP, may influence CD8+ T cell immunodominance.
  • Specific flanking residues play a role in the efficiency of peptide epitope transport by the TAP complex.

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