A RECOMBINANT, SOLUBLE, SINGLE-CHAIN CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX MOLECULE WITH BIOLOGICAL-ACTIVITY

Heterodimeric class I major histocompatibility complex molecules, which consist of a 45-kDa heavy-chain and a 12-kDa beta2-microglobulin (beta2m) light chain, bind endogenously synthesized peptides for presentation to antigen-specific T cells. We have synthesized a gene encoding a single-chain, soluble class I molecule derived from mouse H-2D(d), in which the carboxyl terminus of beta2m is linked via a peptide spacer to the amino terminus of the heavy chain. The chimeric protein is secreted efficiently from transfected L cells, is thermostable, and when loaded with an appropriate antigenic peptide, stimulates an H-2D(d)-restricted antigen-specific T-cell hybridoma. Thus, functional binding of peptide does not require the complete dissociation of beta2m, implying that a heavy chain/peptide complex is not an obligate intermediate in the assembly of the heavy-chain/beta2m/peptide heterotrimer. Single-chain major histocompatibility complex molecules uniformly loaded with peptide have potential uses for structural studies, toxin or fluor conjugates, and vaccines.