Abstract
Pokeweed antiviral protein (PAP) is a 29 kDa type I ribosome inactivating protein (RIP) found in pokeweed plants. Pokeweed produces different forms of PAP. This review focuses on the spring form of PAP isolated from Phytolacca americana leaves. PAP exerts its cytotoxicity by removing a specific adenine from the α-sarcin/ricin loop of the large ribosomal RNA. Besides depurination of the rRNA, PAP has additional activities that contribute to its cytotoxicity. The mechanism of PAP cytotoxicity is summarized based on evidence from the analysis of transgenic plants and the yeast model system. PAP was initially found to be anti-viral when it was co-inoculated with plant viruses onto plants. Transgenic plants expressing PAP and non-toxic PAP mutants have displayed broad-spectrum resistance to both viral and fungal infection. The mechanism of PAP-induced disease resistance in transgenic plants is summarized.
Highlights
Pokeweed antiviral protein (PAP), purified from the leaves of pokeweed plant (Phytolacca americana), was found to be a potent inhibitor of eukaryotic protein synthesis [1] and several plant and animal viruses [2,3] more than four decades ago [4]
PAP removes a specific adenine residue from the highly conserved α-sarcin/ricin loop (SRL) in the 28S rRNA of the eukaryotic ribosome [5] by a process termed depurination, which is characteristic of a group of proteins called ribosome inactivating proteins (RIPs)
These results provided further evidence that ribosome depurination and translation inhibition by PAP could be separated from cytotoxicity
Summary
Pokeweed antiviral protein (PAP), purified from the leaves of pokeweed plant (Phytolacca americana), was found to be a potent inhibitor of eukaryotic protein synthesis [1] and several plant and animal viruses [2,3] more than four decades ago [4]. Shiga toxins produced by bacteria Shigella dysenteriae and enterohemorrhagic Escherichia coli (EHEC) [7]. Both type I and type II RIPs are secretory proteins. Other types of RIPs have been described that are not secretory proteins, including the atypical maize RIP MOD with an internal inactivation loop [8,9,10]. Great advances have been made in understanding the cytotoxicity of PAP and PAP-induced disease resistance in plants. These two aspects of PAP will be the focus of this review
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