RIBOSOME-INACTIVATINGPROTEINS: A Plant Perspective

Abstract

Ribosome-inactivating proteins (RIPs) are toxic N-glycosidases that depurinate the universally conserved alpha-sarcin loop of large rRNAs. This depurination inactivates the ribosome, thereby blocking its further participation in protein synthesis. RIPs are widely distributed among different plant genera and within a variety of different tissues. Recent work has shown that enzymatic activity of at least some RIPs is not limited to site-specific action on the large rRNAs of ribosomes but extends to depurination and even nucleic acid scission of other targets. Characterization of the physiological effects of RIPs on mammalian cells has implicated apoptotic pathways. For plants, RIPs have been linked to defense by antiviral, antifungal, and insecticidal properties demonstrated in vitro and in transgenic plants. How these effects are brought about, however, remains unresolved. At the least, these results, together with others summarized here, point to a complex biological role. With genetic, genomic, molecular, and structural tools now available for integrating different experimental approaches, we should further our understanding of these multifunctional proteins and their physiological functions in plants.

Photochemically stimulated drug delivery increases the cytotoxicity and specificity of EGF–saporin

“…RIPs can mainly be divided into 2 groups, type I and type II (Barbieri et al 1993, Nielsen & Boston 2001. Type I RIPs, as gelonin, agrostin and saporin consist only of the cytotoxic chain with N-glycosidase activity (Achain), while type II RIPs, as ricin, abrin and mistelthoe lectin, have a cell binding B chain in addition to the toxic A-chain.…”

Purification and characterization of Moschatin, a novel type I ribosome-inactivating protein from the mature seeds of pumpkin (Cucurbita moschata), and preparation of its immunotoxin against human melanoma cells

“…Plant RIPs are classified into three groups based on their primary structures [9]:Type 1 RIPs, such as Trichosanthin (TCS), are single-chain basic proteins with a molecular weight of ~30 kD; Type 2 RIPs, like ricin, are two-chain proteins that consist of an A-chain with rRNA N-glycosidase activity through a disulfide bond linked to a lectin-like B chain, the molecular weight of each chain being of ~30 kD; Type 3 RIPs, like maize RIP, require natural proteolysis processing to transform the inactive precursors to mature RIPs.…”

Immune-O-Toxins as the magic bullet for therapeutic purposes

“…Based on the existence of the two domains, RIPs can either be holotoxins or hemitoxins. The binding domains of holotoxins ought to be removed by diminution of the disulfide bond preceding translocation of enzymatic counterpart into the cytosol (Shapira and Benhar, 2010;Nielsen and Boston, 2001;Pieumans et al, 2001). On the basis of their structure and mode of activation RIPs can be divided into three sets.…”