Spinal Column Architecture of the Flexible SPP1 Bacteriophage Tail Tube

Phage therapy has recently regained attention at combating multidrug-resistant bacteria. In 2019, tailed bacteriophages of the Siphoviridae family were engineered to successfully treat a disseminated bacterial infection after all other drugs had failed.(1) This family of phages features a long, flexible, non-contractile tail that has been difficult to characterize structurally. Here, we present the atomic structure of the tail-tube of the bacteriophage SPP1 - a member of this family. Our hybrid structure is based on the integration of structural restraints from solid-state NMR and a density map from cryo-EM. We show that the tail tube protein (TTP) gp17.1 organizes into hexameric rings that are stacked by flexible linker domains and, thus, form a hollow flexible tube with a negatively charged lumen suitable for the transport of DNA. One sentence summaryIntegrative structural biology by solid-state NMR and cryo-EM enables structure determination of the flexible tail of the bacteriophage SPP1.