Artem V. Domashevskiy
The City University of New York, USA
Common pokeweed plant (Phytolacca Americana) produces pokeweed antiviral protein (PAP) as a defense mechanism against foreign pathogenic invaders. PAP is a ribosome inactivating protein (RIP) and an RNA N-glycosidase that removes specific purine residues from the sarcin/ricin (S/R) loop of large rRNA, arresting protein synthesis at the translocation step. PAP is also a cap-binding protein, and is a potent antiviral agent against many plant, animal, and human viruses. Our research aims to elucidate the antiviral mechanism of RNA depurination and to understand how PAP recognizes and targets various RNA substrates. We have investigated interactions between PAP and Turnip mosaic virus genome linked protein (VPg). VPg functions as a cap analog in cap-independent translation, and potentially target PAP to uncapped IRES-containing RNA. Fluorescence spectroscopy and HPLC techniques were used to quantitatively describe PAP depurination activity and PAP-VPg interactions. PAP binds to VPg with high affinity (29.5 nM); the reaction is enthalpically driven and entropically favored. Further, VPg is a potent inhibitor of PAP depurination of RNA in wheat germ lysate, and competes with structured RNA derived from tobacco etch virus (TEV) for PAP binding. VPg may confer an evolutionary advantage by suppressing one of the plant defense mechanisms, and also suggests the possible use of this protein against the cytotoxic activity of RIPs.