Mistletoe lectin dissociates into catalytic and binding subunits before translocation across the membrane to the cytoplasm

Hybridomas producing monoclonal antibodies (mAbs) against the mistletoe lec tin A-chain (MLA) were obtained to investigate the intracellular routing an d translocation of ribosome-inactivating proteins. Anti-MLA mAb MNAS did no t bind the holotoxin but interacted with isolated MLA. This epitope,vas not recognized upon MLA denaturation or conjugation of MLA with the ricin bind ing subunit (RTB), Furthermore, the mAbs did not appreciably react with a p anel of MLA synthetic octapeptides linked to the surface of polyethylene pi ns. A study of the cytotoxicity of mistletoe lectin, ricin, and chimeric to xin MLA/RTB for the hybridomas revealed that interchain disulfide bond redu ction and subunit dissociation are required for cytotoxic activity of mistl etoe lectin, (C) 1999 Federation of European Biochemical Societies.