Cryo-EM structure of a Shigella podophage reveals a hybrid tail and novel decoration proteins.

There is a paucity of high-resolution structures of phages infecting Shigella, a human pathogen and a serious threat to global health. HRP29 is a Shigella podophage belonging to the Autographivirinae family, and has very low sequence identity to other known phages. Here, we resolved the structure of the entire HRP29 virion by cryo-EM. Phage HRP29 has a highly unusual tail that is a fusion of a T7-like tail tube and P22-like tailspikes mediated by interactions from a novel tailspike adaptor protein. Understanding phage tail structures is critical as they mediate hosts interactions. Furthermore, we show that the HRP29 capsid is stabilized by two novel, and essential decoration proteins, gp47 and gp48. Only one high resolution structure is currently available for Shigella podophages. The presence of a hybrid tail and an adapter protein suggests that it may be a product of horizontal gene transfer, and may be prevalent in other phages.

Shigella viruses Sf22 and KRT47 require outer membrane protein C for infection.

Viruses rely on hosts for their replication: thus, a critical step in the infection process is identifying a suitable host cell. Bacterial viruses, known as bacteriophages or phages, often use receptor binding proteins to discriminate between susceptible and non-susceptible hosts. By being able to evade predation, bacteria with modified or deleted receptor-encoding genes often undergo positive selection during growth in the presence of phage. Depending on the specific receptor(s) a phage uses, this may subsequently affect the bacteria's ability to form biofilms, its resistance to antibiotics, pathogenicity, or its phenotype in various environments. In this study, we characterize the interactions between two T4-like phages, Sf22 and KRT47, and their host receptor S. flexneri outer membrane protein C (OmpC). Results indicate that these phages use a variety of surface features on the protein, and that complete resistance most frequently occurs when hosts delete the ompC gene in full, encode premature stop codons to prevent OmpC synthesis, or eliminate specific regions encoding exterior loops.