Enzymatic Activities of Ribosome-Inactivating Proteins
Ribosome-inactivating proteins (RIPs) constitute a diverse group of proteins that share an RNA N-glycosidase activity that acts very specifically on the ribosomal RNA of the 50S/60S ribosomal subunit to inhibit protein synthesis. Additionally, the majorit
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Abstract Ribosome-inactivating proteins (RIPs) constitute a diverse group of proteins that share an RNA N-glycosidase activity that acts very specifically on the ribosomal RNA of the 50S/60S ribosomal subunit to inhibit protein synthesis. Additionally, the majority of RIPs act on non-ribosomal RNA and DNA in a sequence context-independent fashion, releasing multiple adenines and sometimes guanines. One such activity depends on the presence of a 50 cap structure, and may be responsible for the anti-viral properties of some RIPs. In addition to their N-glycosidase activity on nucleic acids, some ribosome-inactivating enzymes have been reported to be bifunctional with another, unrelated activity. No active sites for these unrelated activities have been found, and their presence in preparations of RIPs may be due to contamination.
1 Introduction The discovery of the highly specific RNA N-glycosidase activity of RTA (ricin A-chain) (Endo and Tsurugi 1987) and other ribosome-inactivating proteins (RIPs) towards ribosomes was widely regarded as being entirely responsible for their cytotoxic action. However, in recent years this straightforward explanation has been questioned by the finding that many RIPs can act in a much less specific manner on a variety of RNA and DNA substrates, and also possess a number of apparently unrelated activities such as superoxide dismutase, phospholipase, and pectin methylesterase. Clearly, this challenges the notion of the “unity of biochemistry” especially when taking into account the fact that all of the RIPs from diverse sources for which crystal structures exist are essentially similar in structure, with
M.R. Hartley Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK e-mail: [email protected]
J.M. Lord and M.R. Hartley (eds.), Toxic Plant Proteins, Plant Cell Monographs 18, DOI 10.1007/978-3-642-12176-0_3, # Springer-Verlag Berlin Heidelberg 2010
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˚ from RTA (reviewed by Robertus and Monzingo 2004). rms deviations of
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