An in vitro Study of the Dynamic Features of the Major Histocompatibility Complex Class I Complex Relevant to Its role as a Versatile Peptide-Receptive Molecule

• Published in: Proceedings of the National Academy of Sciences - PNAS 1997-12, Vol.94 (25), p.13826-13831
• Main Authors: Horig, Heidi, Papadopoulos, Nicholas J., Vegh, Zsuzsanna, Palmieri, Edith, Angeletti, Ruth H., Nathenson, Stanley G.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Animals; beta 2-Microglobulin - chemistry; beta 2-Microglobulin - genetics; beta 2-Microglobulin - metabolism; Biological Sciences; Cell-Free System; Endoplasmic reticulum; Endosomes; Exchange rates; Gel chromatography; Gels; H-2 Antigens - chemistry; H-2 Antigens - genetics; H-2 Antigens - metabolism; Hydrogen-Ion Concentration; Immunology; In Vitro Techniques; Kinetics; Major histocompatibility complex genes; Mice; Molecular chains; Molecular Sequence Data; Molecules; Oligopeptides - chemistry; Oligopeptides - metabolism; Peptides; Protein Binding; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; T lymphocytes
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.25.13826

The major histocompatibility complex class I complex consists of a heavy chain and a light chain (β2- microglobulin, β2m, which assemble with a short endogenously derived peptide in the endoplasmic reticulum. The class I peptide can be directly exchanged, either at the cell surface or, as recently described, in vesicles of the endocytic compartments, thus allowing exogenous peptides to enter the class I presentation pathway. To probe the interactions between the components of the class I molecule, we analyzed the exchange of peptide and β2m by using purified, recombinant H2-Kb/peptide complexes in a cell-free in vitro system. The exchange of competitor peptide was primarily dependent on the off-rate of the original peptide in the class I binding groove. Peptide exchange was not enhanced by the presence of exogenous β2m, as exchange occurred to the same extent in its absence. Thus, the exchange of peptide and β2m are independent events. The exchange rate of β2m also was not affected by the dissociation rates of the original peptides. Furthermore, peptides could substantially exchange into class I molecules over a pH range of 5.5 to 7.5, conditions prevalent in certain endocytic compartments. We conclude that the dynamic properties of the components of class I molecules explain its function as a highly peptide-receptive molecule. The major histocompatibility complex class I can readily receive peptides independent of the presence of exogenous β2m, even at a low pH. Such properties are relevant to class I peptide acquisition, which can occur at the cell surface, as well as in specialized endosomes.