Professors Michael Norris and Karen Maxwell at the University of Toronto describe a protein found in bacteria, ring-interacting pore 1 (Rip1), that serves as a viral defense mechanism. Rip1 recognizes infecting bacteriophage (viruses that attack bacteria) and then programs the cell to die instead of manufacturing the virus. This protein is part of an old prophage (a previous viral infection that ended up inserting into the chromosome). Rip1 recognizes a conserved step in viral assembly. Rip1 binds to the phage portal protein and others that form scaffolds. The portal protein serves as a starting point for capsid formation and is essential for genome packaging and viral release. Rip1 activates when ring-shaped complexes that are essential for virion maturation begin to form. Rip1 then uses these complexes to assemble into membrane-spanning pores. This has two effects.
- When Rip1 inserts into these ring-shaped scaffolds, it disrupts the viral assembly process, inhibiting viral synthesis.
- The Rip1 complex formed is a pore that can insert into the membrane, causing the host cell to die prematurely and preventing productive viral replication.
This is an incredibly simple defense mechanism, since it only needs one 164 amino acid protein to counteract dozens of phages that use this assembly process. Rip1-like proteins are present in a wide variety of bacteria, with a search revealing more than 4,100 bacteria with similar sequences. The research article was published in Nature.