Evidence for peptide transport across microsomal membranes

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• T-cell receptors recognize peptides bound to Major Histocompatibility Complex (MHC) class I molecules during antiviral immune responses.
• The recognition of peptides from both cytoplasmic and membrane viral proteins implies a pathway for transporting peptides from the cytosol to MHC class I assembly compartments.

Purpose of the Study:

• To investigate the pathway for transporting peptides into the compartment where MHC class I molecules assemble.
• To develop and utilize an in vitro assay for studying peptide transport into microsomal vesicles.

Main Methods:

• Development of an in vitro assay using chemically synthesized peptides (13-21 amino acids) with N-linked glycosylation acceptor sequences.
• Incubation of peptides with microsomal vesicles and monitoring the depletion of dolichol high-mannose oligosaccharides in the lumen.
• Testing for ATP dependence using apyrase and an ATPase inhibitor.

Main Results:

• Demonstrated transport of specific antigenic peptides (HIV gag, influenza B nucleoprotein) into microsomal vesicles.
• Observed depletion of dolichol high-mannose oligosaccharides, indicating peptide transport and glycosylation substrate utilization.
• Transport was not dependent on ATP, contrary to expectations based on homologous ATP-binding cassette transporters.

Conclusions:

• The study provides evidence for a specific in vitro peptide transport pathway into microsomal vesicles.
• The observed specificity suggests a regulated process for selecting peptides for transport.
• The lack of ATP dependence challenges current models involving ATP-binding cassette transporters in this specific peptide transport mechanism.