Reconstruction of the phi24B Stx-Converting Bacteriophage Axial Fibril Using Cryo-Electron Microscopy

The structure of the gp56 axial fibril forming part of the adsorption apparatus of the phi24B Stx-converting phage was studied using cryo-electron microscopy. The axial fibril is highly mobile, and the gp56 trimer is surrounded by the massive complex of the gp57 nozzle protein hexamer, which creates a symmetry mismatch at the interface and makes it difficult to obtain a three-dimensional reconstruction. Using the symmetry expansion approach and local refinement, we have generated a density map of the axial fibril, visualized the tertiary structure of its globular domains, and determined their location relative to the other proteins of the phi24B adsorption apparatus.