PROTEIN-PRODUCTION BY THE FILAMENTOUS FUNGUS TRICHODERMA-REESEI - SECRETION OF ACTIVE ANTIBODY MOLECULES

Trichoderma reesei is used by industry for production of plant materia l hydrolysing enzymes, especially cellulases. The fungus has excellent production and secretion capacity. The major cellulase cellobiohydrol ase I (CBHI) represents half of the protein secreted and is encoded by a single copy gene. The strong cbh1 promoter and other promoters regu lated in a different manner are available for protein production. The potential of the fungus in foreign protein production has been demonst rated by the expression of chymosin, interleukin-6, and laccase. Antib odies and their engineered forms have numerous applications. The capac ity of Trichoderma to produce different forms of antibodies such as Fa b molecules under the cbh1 promoter was analysed. When light chain was produced alone the secreted yields were very low but could be increas ed by introducing the heavy-Fd chain into the fungus. When the heavy-F d chain was fused to the C-terminus of the CBHI core-linker region, pr oduction of secreted Fab's was increased about 50-fold. The amount of immunologically active CBHI-Fab molecules was about 150 mg/L in the me dium in a fermenter cultivation. The released Fab molecules were authe ntic in their immunological properties demonstrating functional assemb ly of the light and heavy chains. The antibody part can be released fr om the CBHI fusion by an unidentified fungal protease or Kex2. The ben eficial role of CBHI could be explained by more efficient transcriptio n, ER entry or folding, or passage through the secretory pathway in ge neral.