Structural Superimposition

Abstact

Carbapenem-resistant Klebsiella pneumoniae is a critical-priority pathogen, underscoring the need for alternatives to antibiotics. Bacteriophages are promising agents, yet high-resolution structures of K. pneumoniae phages are scarce. Here, we report near-complete cryo-electron microscopic reconstructions of the K. pneumoniae podophage RAN69 at 3.0-3.4 A resolution, enabling atomic models for 12 structural components. Complete in situ structures of the long tail fiber (gp9 trimer) and distal tail spike (gp1 trimer) are resolved, revealing a previously unknown binding interface in which the gp1 N-terminal arm wedges between spike-binding domains of gp9. The pre-ejectosome forms a conserved double-layered assembly (gp10 tetramer over gp11 octamer), tethered to the portal by an octameric gp12 that inserts long helices into the portal barrel, with gp20 reinforcing gp11 interfaces. Divergent folds in gp10 and a lysozyme-like gp11 peripheral domain suggest adaptation to host envelopes. These structures advance our understanding of podophage assembly.