Peptide length preferences for rat and mouse MHC class I molecules using random peptide libraries

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Major histocompatibility complex (MHC) class I molecules present peptides to CD8+ T cells.
• Conserved polar residues in human and mouse MHC class I grooves typically bind short peptides.
• Unusual residues in rat MHC class I suggest potential for binding longer peptides.

Purpose of the Study:

• To investigate the peptide length preferences of two rat MHC class Ia molecules, RT1-A1c and RT1.Aa.
• To determine if unique residues in RT1-A1c facilitate binding of longer peptides compared to canonical rat MHC class I.

Main Methods:

• Utilized the TAP2-deficient mouse cell line RMA-S for expressing rat MHC class Ia molecules.
• Employed temperature-dependent peptide stabilization assays with synthetic random peptide libraries (7-15 amino acids).
• Quantified peptide stabilization using Fluorescence-Activated Cell Sorting (FACS) analysis.

Main Results:

• Mouse MHC class I molecules H2-Kb and H2-Db showed distinct length preferences (8-13-mer and 9-15-mer, respectively).
• Rat RT1.Aa molecule preferred 9-15-mer peptides.
• Rat RT1-A1c molecule exhibited a stricter preference for 9-12-mer peptides, not longer ones.

Conclusions:

• The hypothesis that unusual residues in rat MHC class I molecules enable binding of longer peptides was refuted.
• Peptide length preference in rat MHC class Ia molecules is influenced by specific residues within the peptide-binding groove.
• RT1-A1c demonstrates a more restricted peptide length repertoire than RT1.Aa, despite possessing unique groove residues.