Mutations in the hydrophobic domain of poliovirus protein 3AB abrogate its permeabilizing activity

Poliovirus protein 3AB contains a predicted amphipathic helix that could lead to pore formation in membranes. We have introduced various mutations in the hydrophobic domain of the protein and the membrane-modifying properties of the resulting mutants have been analyzed. Expression of wild type 3AB protein in E. coli increases the influx and efflux of different molecules such as nucleosides, lactose analogues and antibiotics. Thus, 3AB expression makes E. coli cells two orders of magnitude more sensitive to hygromycin B, a non-permeant inhibitor of translation, and causes a 15-20-fold enhancement in the efflux of uridine. Changes in membrane permeability take place under conditions where no cellular lysis is detected and when other molecules such as beta-galactosidase or polyribonucleotides are kept inside the cell. These membrane modifications can be blocked to different extents by amino acid substitutions in the membrane-spanning region of the protein. These results suggest that poliovirus protein 3AB could possess an intrinsic ability to form pores in natural membranes, thus allowing the flux of small hydrophylic molecules through them.