FIORENZO STIRPE:  FRIDAY 31 MARCH 2006, 09:45

Ribosome-inactivating proteins as components of immunotoxins: advances, pros and cons

Fiorenzo Stirpe
Università di Bologna, Dipartimento di Patologia sperimentale, Bologna, Italy

Ribosome-inactivating proteins are enzymes, so far isolated only from plants, which remove adenine from rRNA and other polynucleotide substrates. They can be divided into two main categories, type 1 consisting of a single chain with enzymatic activity, and type 2, consisting of and enzymatically active A chain linked to a B chain with lectin properties. The latter binds to sugar-terminated receptors on the surface of most cells, allowing the entry into the cytoplasm of the A chain, which kills the cells by damaging ribosomes and possibly other structures. Thus several type 2 RIPs are potent toxins (ricin and related toxins), whereas type 1 RIPs are much less toxic, because they enter with difficulty inside cells. Both type 1 RIPs and the A chains of type 2 RIPs are linked to, or fused with, antibodies or other carriers to form immunotoxins or other conjugates specifically toxic to the cells target of the carriers. These conjugates can be use as experimental tools and are tested for possible therapeutic applications, especially for the therapy of cancer.
The properties of RIPs will be discussed, with emphasis on recent advancements, together with the advantages and limitations of their use as components of conjugates.

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