Conformational dynamics of the beta(2)-microglobulin C terminal in the cell-membrane-anchored major histocompatibility complex type I

We have recently described an anti-beta(2)-microglobulin (beta 2-m) monoclo nal antibody (mAb 14H3) capable of recognizing the epitope 92-99 of the pro tein in the monomeric native state as well as in the fibrillar polymeric st ate, 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 beta 2-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 mu M. An interaction between the complex and the membrane protects beta 2-m from immunological recognition at the MHCI level. This protection from antibody recognition can be weakened by procedu res such as heat shock or gamma irradiation that perturb the membrane struc ture and commit the cell to the apoptotic pathway. mAb 14H3 can recognize M HCI in a transient state that most likely precedes beta 2-m shedding and ma y be proposed as a useful tool for dynamic analysis of MHCI conformational modifications.