Conformational dynamics of the β2-microglobulin C terminal in the cell-membrane-anchored major histocompatibility complex type I

We have recently described an anti-β₂-microglobulin (β2-m) monoclonal antibody (mAb 14H3) capable of recognizing the epitope 92-99 of the protein in the monomeric native state as well as in the fibrillar polymeric state, but not in the major histocompatibility complex type I (MHCI) anchored to the cell membrane. In the present study, we investigated the molecular basis for the inaccessibility of the C-terminal end of β2-m in the MHCI complex, and demonstrated that mAb 14H3 binds the soluble fraction of the MHCI complex with a K(d) of 0.3 μM. An interaction between the complex and the membrane protects β2-m from immunological recognition at the MHCI level. This protection from antibody recognition can be weakened by procedures such as heat shock or γ irradiation that perturb the membrane structure and commit the cell to the apoptotic pathway. mAb 14H3 can recognize MHCI in a transient state that most likely precedes β2-m shedding and may be proposed as a useful tool for dynamic analysis of MHCI conformational modifications.