Cryo-EM study of the pseudomonas bacteriophage φKZ

The phi KZ virus is one of the largest known bacteriophages. It infects Pseudomonas aeruginosa, which is frequently pathogenic in humans, and, therefore, has potential for phage therapy. The phi KZ virion consists of an 1450 A diameter icosahedral head and an 2000 A long contractile tail. The structure of the phi KZ tail has been determined using cryo-electron microscopy. The phi KZ tail is much longer than that of bacteriophage T4. However, the helical parameters of their contractile sheaths, surrounding their tail tubes, are comparable. Although there is no recognizable sequence similarity between the phi KZ and T4 tail sheath proteins, they are similar in size and shape, suggesting that they evolved from a common ancestor. The phi KZ baseplate is significantly larger than that of T4 and has a flatter shape. Nevertheless, phi KZ, similar to T4, has a cell-puncturing device in the middle of its baseplate.