Chapter 22 - Fungal Ribosome Inactivating Proteins

Abstract

This chapter focuses on fungal ribosome inactivating proteins (RIPs). These proteins were isolated from a number of fungi including Aspergillus and Trichoderma spp. and several mushrooms. Ribosome inactivating peptides found in Cucurbitaceous seeds have not been detected in fungi. The smallest fungal RIP isolated to date, velutin—from the mushroom (basidiomycete fungus) Flammulina velutipes—has a molecular mass of about 14kDa. Small RIPs with a molecular mass of approximately 20kDa, and RIPs about 30kDa in molecular mass, are found in both fungal and plant RIPs. The Aspergillus RIPs are ribonucleases with highsequence homology. In contrast, most mushroom RIPs do not show structural resemblance to each other and have little or no ribonuclease activity. All fungal RIPs demonstrate potent inhibitory activity in the cell-free translation system. Other activities of fungal RIPs include mitogenic/antimitogenic activity toward splenocytes and antiproliferative activity toward tumor cells. RIPs probably serve a role of defense in fungi. RIPs manifest an array of biological activities including translation-inhibitory, N-glycosidase, antimitogenic, immunomodulatory, antiproliferative, and antifungal activities. RIP-based immunotoxins have been constructed and used in cancer therapy. Transgenic plants carrying the RIP gene are less susceptible to viral infections.