Abstract

Ribosome-inactivating proteins (RIPs) are toxins that act as N-glycosidases (EC 3.2.2.22). They are mainly produced by plants and classified as type 1 RIPs and type 2 RIPs. There are also RIPs and RIP related proteins that cannot be grouped into the classical type 1 and type 2 RIPs because of their different sizes, structures or functions. In addition, there is still not a uniform nomenclature or classification existing for RIPs. In this review, we give the current status of all known plant RIPs and we make a suggestion about how to unify those RIPs and RIP related proteins that cannot be classified as type 1 or type 2 RIPs.

Highlights

  • Because of their N-glycosidase activity, ribosome-inactivating proteins inhibit protein synthesis by cleaving a specific adenine residue (A4324) from the 28S ribosomal RNA of the large 60S subunit of rat ribosomes followed by cell death [1]

  • There are Ribosome-inactivating proteins (RIPs) and RIP related proteins that cannot be grouped into the classical type 1 and type 2 RIPs because of their different sizes, structures or functions

  • Beside the peculiar type 1 RIPs, b-32 and JIP60, there is a certain amount of other proteins that cannot be grouped into the classical type 1 or type 2 RIPs, because of structural and functional differences

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Summary

Introduction

Because of their N-glycosidase activity, ribosome-inactivating proteins inhibit protein synthesis by cleaving a specific adenine residue (A4324) from the 28S ribosomal RNA of the large 60S subunit of rat ribosomes followed by cell death [1]. In some cases, the same term was used to designate different proteins, e.g., the term momordin II was used for a protein from Momordica balsamina as well as for a protein from Momordica charantia or the term MAP was used for a protein (MAP 30) from Momorica charantia and for a protein from Mirabilis jalapa (MAP = Mirabilis antiviral protein) These examples are intended to illustrate that there is still no unambiguous nomenclature for the RIPs. There are ambiguities about the classification of some proteins, whether they are type 2 RIPs or just lectins, because no assay concerning the toxicity was performed or there was no information given about the structure: SGSL from Trichosanthes anguina, TCSL from Trichosanthes cucumerina, TKL-1 from Trichosanthes kirilowii, TDSL from Tichosanthes dioica, and BDA from Bryonia dioica. We focused on RIPs from plants, whereas other RIPs from algae, bacteria, and fungi are not considered further

Table of RIPs from plants
Exceptions Prove the Rule
Small RIPs
RIP Candidates and RIP-Like Proteins
Non-Toxic Type 2 RIPs
Demotion of Some RIPs
Conclusions
Conflicts of Interest
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