Pokeweed Antiviral Protein

1. Pokeweed Antiviral Protein

2. Pokeweed • Pokeweed is a common plant - Phytolacca americana • It has many uses which include dyes, colours for wines and sweets, and can also be eaten as a vegetable. • To add to these uses PAP – pokeweed antiviral protein has been isolated.

3. PAP PAP- pokeweed antiviral protein Isolated from the cell walls of the plant Phytolacca americana • Its a single-chain (type I) ribosome-inactivating protein (RIP) that depurinates ribosome's at the sarcin/ricin loop of the large rRNA subunit of ribosomes, resulting in inhibition of translation by halting the elongation step.

4. PAP • Mature pokeweed antiviral protein has an A (active) chain but lacks a B (binding) chain. • Precursors have the A and B chain but B is cleaved so that chain A can become active. • Without this B chain to mediate cell membrane binding, the toxin PAP cannot enter the cell. • By conjugating the protein to a monoclonal antibody or a lectin, the substance can be bound to a cell membrane and internalized where it acts to inhibit protein synthesis. (Irvin et al 1980)

5. PAP -how its gets into the cytosol • Ulku Baykal, Nilgun E. Tumer (2007) used a series of PAP mutants to identified a C-terminal signal. They showed that type 1 RIPs have common signal pathways to enter the cytosol with type 2 RIPs, and that a sequence at the C-terminus of type 1 rips mediates its transport to the cytosol • Ulku Baykal et.al suggests the C-terminal sequence may bind to membrane lipids, facilitating insertion of PAP into membranes. Pokeweed antiviral protein may unfold as a result of an interaction with the lipid membrane and the unfolded protein may be transported into cytosol. • The mature form of PAP is retro-translocated from the ER into the cytosol where it escapes degradation unlike the other substrates of the retro-translocation pathway.

6. PAP • James D. Irvin and Gary M. Aron 1982 describes how pokeweed has been used successfully inhibit the production of mammalian viruses in tissue culture. • Ulku Baykal, Nilgun E. Tumer (2007) Have done some research showing the effect of Progressive deletion of amino acids from the C-terminus of mature PAP demonstrated that C-terminal residues 250–262 of the mature protein were critical for its accumulation in the cytosol.

7. PAP Bijal A. Parikh,Ulku Baykal Rong Di, and Nilgun E. Tumer (2005) discusses the analysis of the variant protein, N70A, near the active-site which is required for depurination of cytosolic ribosomes but not for cap binding or mRNA destabilization, indicating that the activity of PAP on capped RNA can be uncoupled from its activity on rRNA. These findings suggest that the altered active site of PAP might accommodate a narrower range of substrates, thus reducing ribotoxicity while maintaining potential therapeutic benefits.

8. references • Jeffrey L. Brodsky, Ph.D.* and Richard J.H. Wojcikiewicz, Ph.D.. (2009). Substrate Specific Mediators of ER Associated Degradation (ERAD). • Bijal A. Parikh,‡§ Ulku Baykal,§ Rong Di,§ and Nilgun E. Tumer*‡§. (2005). Evidence for Retro-Translocation of Pokeweed Antiviral Protein from Endoplasmic Reticulum into Cytosol and Separation of Its Activity on Ribosomes from Its Activity on Capped RNA. biochemistry. 44 (7). • Oleg Zoubenko1, Fatih Uckun2, Yoonkang Hur1, IIan Chet3 & NilgunTumer. (1997). Plant resistance to fungal infection induced by nontoxic pokeweed antiviral protein mutants. Nature - Biotechnology. 15 (10), • Ulku Baykal, Nilgun E. Tumer. (2007). The C-terminus of pokeweed antiviral protein has distinct roles in transport to the cytosol, ribosome depurination and cytotoxicity. The Plant journal. 49 (6), 995–1007.