Inhibition of Poliovirus Replication by a Plant Antiviral Peptide *

A novel mechanism for inhibition of translation by pokeweed antiviral protein: Depurination of the capped RNA template

“…Pokeweed antiviral protein (PAP), a 29-kDa protein isolated from the leaves of the pokeweed plant, Phytolacca americana, is a strong inhibitor of protein synthesis and belongs to a family of proteins called ribosomeinactivating proteins (RIPs)+ PAP is a type I RIP that consists of a single polypeptide chain+ Type II RIPs, such as ricin, have a catalytic A-chain that is joined to a B-chain, which comprises a galactose-binding lectin+ RIPs are known to inactivate ribosomes by depurination of a specific adenine from the highly conserved, surface exposed, sarcin/ricin (S/R) loop of the large rRNA of eukaryotic and prokaryotic ribosomes Hartley et al+, 1991)+ This modification affects the binding and GTPase activity of the two elongation factors, eEF-1 and eEF-2, thereby blocking protein synthesis at the translocation step (Montanaro et al+, 1975;Osborn & Hartley, 1990)+ PAP exhibits potent antiviral activity against both plant and animal viruses (Tomlinson et al+, 1974;Ussery et al+, 1977;Aron & Irvin, 1980;Zarling et al+, 1990)+ Based on the extracellular location of PAP and the correlation between antiviral activity and ribosome depurination, it has been proposed that PAP enters the cell along with the virus and inhibits virus multiplication by inactivating host ribosomes, resulting in local suicide at the site of infection (Ready et al+, 1986;Chen et al+, 1993;Taylor et al+, 1994)+ However, studies with animal viruses suggest that the antiviral action of PAP may not be due to its inactivation of ribosomes (Zarling et al+, 1990)+ We have previously isolated nontoxic PAP mutants with changes in the N-and C-terminal sequences, as well as at the active site (Hur et al+, 1995)+ A nontoxic C-terminal deletion mutant of PAP (PAPc), which does not depurinate host ribosomes, exhibits antiviral activity when expressed in transgenic plants, providing further evidence that antiviral activity of PAP can be dissociated from depurination of host ribosomes (Tumer et al+, 1997)+ As antiviral activity can be separated from ribosome depurination, PAP may well be able to act on substrates other than rRNA+ Alternative substrates and enzymatic activities of some RIPs have been recently described+ It has been shown that saporin-L1 from Saponaria officinalis could depurinate a variety of polynucleotides (Barbieri et al+, 1996)+ To date, more than 50 RIPs tested were capable of depurinating DNA, RNA, and poly (A) RNA (Barbieri et al+, 1997)+ Some RIPs were reported to hydrolyze single-stranded and doublestranded DNA (Li et al+, 1991;Huang et al+, 1992;Ling et al+, 1994;Nicolas et al+, 1997), and we recently showed that PAP cleaves double-stranded supercoiled DNA using the same active site required to depuri...…”

Insights into the Molecular Antiviral Mechanism of Pokeweed Protein from Phytolacca americana

“…The pokeweed plant produces several isozymes of PAP, all exerting potent antiviral properties [11,13,[36][37][38][39][40][41][42]. PAP isozymes evoke depurination of genomic HIV-1 RNA [43][44][45], TMV RNA [46], poliovirus [47], herpes simplex virus (HSV) [48], influenza virus [49], and brome mosaic virus (BMV) [50], among many others, showing a broad spectrum of antiviral activity [13]. This depurination is concentration dependent.…”

“…Interestingly, PAP also exerts its inhibitory effects on the replication uncapped viruses such as influenza and poliovirus [47,49]. Vivanco et al [55] have inspected PAP activity against a set of capped and uncapped viral RNAs, demonstrating that PAP does not depurinate every capped RNA, while inhibiting translation of uncapped viral RNAs in vitro without causing measurable depurination at multiple sites.…”

Inhibition of Pokeweed Antiviral Protein (PAP) by Turnip Mosaic Virus Genome-linked Protein (VPg)

“…This may be the primary mechanism for PAP antiviral activity (20); however, it does not clarify the inhibitory effects of PAP on the replication of uncapped viruses, such as influenza (17) and poliovirus (15). Further, PAP does not depurinate every capped RNA, and it can inhibit translation of uncapped viral RNAs in vitro without causing detectable depurination at multiple sites (21).…”

“…PAP isoforms cause a concentration-dependent depurination of HIV-1 (13), tobacco mosaic virus (14), poliovirus (15), HSV (16), influenza (17), and brome mosaic virus RNAs (18).…”