Class I MHC Is Stabilized Against Thermal Denaturation by Physiological Concentrations of NaCl

• Published in: Biochemistry (Easton) Vol. 39; no. 30; pp. 9030 - 9038
• Main Authors: Batalia, Michael A, Kirksey, Timothy J, Sharma, Ashwani, Jiang, Lihong, Abastado, Jean-Pierre, Yan, Shuqin, Zhao, Rui, Collins, Edward J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.08.2000
• Subjects: Amino Acid Sequence; Animals; beta 2-Microglobulin - chemistry; beta 2-Microglobulin - metabolism; CHO Cells - metabolism; Cricetinae; Dose-Response Relationship, Drug; Drug Stability; Histocompatibility Antigens Class I - chemistry; Histocompatibility Antigens Class I - metabolism; HLA-A2 Antigen - chemistry; HLA-A2 Antigen - metabolism; HLA-D Antigens - chemistry; HLA-D Antigens - metabolism; Hot Temperature; Humans; Osmolar Concentration; Protein Denaturation - drug effects; Sodium Chloride - chemistry; Sodium Chloride - pharmacology
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi000442n

Class I MHC molecules are ternary complexes composed of an allotype specific heavy chain, a noncovalently associated protein β2-microglobulin (β2m), and a peptide. The complexes are assembled in the endoplasmic reticulum by a complex series of chaperones and peptide-loading mechanisms. In the absence of β2m or peptide, very little class I heavy chain is transported to the surface of the cell. Complexes that do not contain all three parts of the protein are not made productively in vivo and not at all in vitro. The ability of the complex to withstand thermal denaturation in vitro has been shown to be related to the binding affinity of the peptide. Paradoxically, some low-affinity peptide complexes denature at or below human basal body temperatures in vitro but are effective biological agents in vivo. Here we show that these complexes are stabilized against thermal denaturation by physiological cosolvents and maximally stabilized by 150 mM NaCl. While the degree of stabilization by 150 mM NaCl is greatest for low-affinity peptide/MHC complexes, the mechanism of stabilization is independent of peptide sequence. This effect is hypothesized to occur by multiple mechanisms including increasing the affinity of β2m for the complex and charge screening.