Pokeweed Antiviral Toxin - Manual

Pokeweed antiviral protein is prepared from the leaves of Phytolacca americana It has been shown to have both antiviral (Irvin, 1983) and anticellular (Irvin 1983, Irvin and Aron 1982, and Cawley et al. 1979) activity. The site of action for the toxin has been shown in cell-free lysates to be at the ribosomes and specifically the EF-2 mediated translocation step of the elongation cycle during protein synthesis. The protein isolated from leaves exists as two forms, Pokeweed Antiviral Protein (PAP) at a molecular weight of 29,000 and PAP II at a molecular weight of 30,000 (Irvin et al 1980)

Classical plant toxins such as ricin or abrin are composed of two functionally active fractions. The A chain contains the toxic activity and the B chain gives the toxin a cell recognition and binding function to facilitate transport across the cell membrane. The A chain is not active until it is internalized by the cell, where it halts protein synthesis. Pokeweed antiviral protein is a hemitoxin which has the A chain activity but lacks a B chain. Without this B chain to mediate cell membrane binding, the toxin 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.

When used with a cell-free lysate, Worthington Pokeweed Antiviral Toxin can inhibit protein synthesis in vitro. When coupled to a monoclonal antibody the toxin can be internalized and be used to inhibit cellular or viral protein synthesis. This data can be further used to illustrate specific steps in the regulation of protein synthesis.