RECONSTITUTION BY MHC-RESTRICTED PEPTIDES OF HLA-A2 HEAVY-CHAIN WITH BETA-2-MICROGLOBULIN, INVITRO

CYTOTOXIC T lymphocytes kill virally infected cells when they detect antigenic fragments presented by class I major histocompatibility complex (MHC) antigens (HLA in humans). The crystal structures of HLA-A2 and HLA-Aw68 reveal that peptide-antigen forms an integral part of the HLA structure, being retained in a prominent groove even after purification and crystallization 1-3. Here we report that the heavy chain and beta-2-microglobulin of HLA-A2, after separation and fractionation in denaturants, reassemble efficiently under renaturing conditions only in the presence of MHC-restricted 4 peptides. A complex of heavy chain, beta-2-microglobulin, and viral peptide in the ratio 1:1:1 is formed in up to 46% yield. Reconstitution is not stimulated by either of two peptides not restricted to HLA-A2. The reconstituted complex of HLA-A2 and the influenza virus (B/Lee/40) nucleoprotein peptide, Np (85-94), crystallizes under conditions previously used to crystallize HLA-A2 (ref. 5). Peptide-linked folding and assembly suggests mechanisms for the unusual capacity of HLA to bind many peptides of diverse sequence.